Chittering sound from drivebelt area at < 1500 rpm

[prwood]

I replaced my alternator and power steering pump a week ago, and since then there has been a chittering sound coming from the drivebelt area whenever the engine is running under 1500rpm. The sound is present both when the AC compressor clutch is engaged and when it's not, although when the clutch is engaged it gets a lot noisier. As far as I'm able to observe, I'm not having any functional issues with the alternator, power steering pump, or ac compressor.

I made a video so you can hear the sound and see the drivebelt area:

https://photos.smugmug.com/Cars/2001-Vo ... 42-640.mp4

The current belt was installed 7/9/2016 and is a "Carquest by Dayco Poly Rib Belt". We have put about 18,000 miles on it since that time. During that time, it has been removed and reinstalled several times for various reasons:

- alternator replacement (replaced 8/5/2017 with Carquest remanufactured model)
- power steering pump replacement (replaced 8/5/2017 with junkyard part)
- timing belt replacement (replaced 7/29/2017 with Gates kit incl water pump and tensioner/idler pulleys)

In some of these cases it was taken off and put back on several times due to having to back-out part of a job.

I haven't done any work with the AC compressor, but I did find a plate on it saying it was manufactured in 2011.

Any thoughts as to what could be causing this sound?

[abscate]

Great audio quality on video - Ive almost given up on trying to diagnose sounds on videos..

That is definitely correlated to the AC compressor pulling in so I would guess either the AC compressor bearing (ouch) or...the serpentine belt idler pulley.

Get a piece of garden hose or PVC hose, stick one end in your ear, and use the other as a stethoscope to isolate the noise location. Listen around until you get the feel of the sound through the hose, its different than what you hear from distance.

If you use garden hose, it should match your car colour. Ok, I made that up.

[prwood]

Will try to isolate the sound. Hoping it has nothing to do with the AC compressor. I'm neither equipped or interested in working on that component. :-\

The serpentine belt doesn't have an idler pulley on this car (only on models without AC).

Great audio quality on video - Ive almost given up on trying to diagnose sounds on videos..

That is definitely correlated to the AC compressor pulling in so I would guess either the AC compressor bearing (ouch) or...the serpentine belt idler pulley.

Get a piece of garden hose or PVC hose, stick one end in your ear, and use the other as a stethoscope to isolate the noise location. Listen around until you get the feel of the sound through the hose, its different than what you hear from distance.

If you use garden hose, it should match your car colour. Ok, I made that up.

[abscate]

Crap on rye bread. I was hoping it was idler. Well, definitely confirm with garden hose - maybe it is one of the relatively cheap components.

You could wait until fall, then try a real quick shot of WD40 on the BACK of the clutch to see if you can lube the bearing a bit until next summer.

Compressor replacement isnt too bad but does require a lot of tools.

Wait - hold the phone - you have to have a tensioner on that - thats what I meant by idler. Still hope for a cheap and easy fix.

[prwood]

Yes, there is a tensioner pulley. If that's it I can replace it with no problem. Will try to confirm with the garden hose method. (I also have one of those stethoscopes with the metal probe, but I think that requires you to be touching the thing you want to listen to, which I don't think would be safe to do with a rotating drivebelt.)

I've replaced the power steering pump and alternator, so I know how to get at the compressor, but my main concern would be with draining the refrigerant. I'd probably have to take it to a shop to have that done... and then back again to have it refilled.

The critical question is whether the sound is just a sound that I could choose to put up with, or if it's an indicator of a component with imminent failure.

Crap on rye bread. I was hoping it was idler. Well, definitely confirm with garden hose - maybe it is one of the relatively cheap components.

You could wait until fall, then try a real quick shot of WD40 on the BACK of the clutch to see if you can lube the bearing a bit until next summer.

Compressor replacement isnt too bad but does require a lot of tools.

Wait - hold the phone - you have to have a tensioner on that - thats what I meant by idler. Still hope for a cheap and easy fix.

[jbeebo]

I've not had great luck with the garden hose as a diagnostic tool mainly because it's hard to hold the open end where you'd like to. I've used mechanics stethoscopes with good success. Am also hoping (and believing) it's the serpentine tensioner or idler bearing, which is far more likely to fail than the AC compressor bearing.

If it is the AC compressor bearing, I'd run that thing until you just can't stand the noise anymore. The proper way is to have the system evacuated, refrigerant recovered and disposed of according to law and after the repair is made, evacuation and fill. You may want to change the filter-dryer too while you're in there and if the system will be open to atmosphere for more than a few hours.

[prwood]

FYI: I had forgotten that I made a better recording with the video stabilized and also showing the difference when revving to 2krpm. I'm narrating in the background but it's barely audible, so basically I'm just saying this is a video with the AC compressor running and then revving the engine up from idle (~675) up to 2krpm. Not sure if it will make any difference in diagnosis. I'm at work so I can't do any other tests at the moment.

https://photos.smugmug.com/Cars/2001-Vo ... 50-640.mp4

edit: original link was to the old video, this is the correct link.

[abscate]

Well at 00:50 your compressor pulls in and the noise returns really clearly.

I would monitor and drive that. If you can find someone who will evacuate your AC, I can loan you the manifold and pump to do that yourself - it isnt hard if it isnt leaking. If you keep the system open for less than 24 hours, you don't need to replace anything other than the compressor.

[SuperHerman]

Pull the belt and spin the tensioner pulley and A/C pulley and see what they feel like. Check for play and how easy that tensioner pulley spins. If the tensioner pulley spins freely and you have excessive axial play the grease is basically gone and/or the bearings may be shot. Usually the tensioner itself will be fine with the pulley bearing being the only issue - but it can also go bad.

One test before dismantling, which may not be definitive, is to cover the belts and spray WD40 or equivalent on the tensioner pulley after removing the protective cap trying to keep what ever liquid from hitting the belts while trying to get something into the bearings. The pulley has a sealed bearing but it is worth a shot at least to find the cause of your noise. Wipe and clean and reinstall cap - then start car and listen.

If you replace just the pulley bearing on the tensioner you may encounter an issue with the replacement pulley. On my XC90 2.9T I just did the replacement using a URO branded pulley. The pulley fits and works just fine, but I could not get the supplied protective plastic cover on as the bolt head sticks out too far for the supplied protective plastic cap and the original cap, which has a more pronounced dome to accommodate the bolt head protrusion, does not fit on the URO branded pulley. I just left it off. Something to be aware of if you just replace the pulley with a non OEM pulley.

My thoughts are this - as the tensioner pulley has not been replaced per your repair list, regardless of whether it is the issue, spending $15 (URO pulley I bought) and proactively replacing it would not hurt and will definitively tell you what your problem is.

Finally, if you have time to burn and don't mind the process, you can take off the tensioner pulley and carefully remove one side of the bearings seals - and I mean carefully - then clean and regrease if the bearings don't look bad. If you are not careful you will bend the seal and/or tear and nick it. That is why I limit my work to only one side - if you are brave do both and then you can really repack the bearing. Don't over pack it with grease - it is not suppose to be full. As you are working on only one side you have to work the grease in by spinning it in hoping some will pass through to the other side. Then reinstall the seal and have this side out so that the protective plastic cap covers it to block any excessive grease from flying all over. I have done this in the past to tie me over until the pulley can be ordered and replaced and to eliminate causes of similar noises. Plus it keeps the car on the road. To each their own.

On the A/C - I believe with the right tools you can do this in car but may need to disconnect the A/C compressor from its mounts but leaving the lines connected to gain space to work. You then take off the clutch and bearing and replace it as a complete, but expensive unit, or see if you can just find a bearing and replace just it. I have seen just a bearing replacement done for other cars so you should be able to do it on yours. Nothing magical about a Volvo AC compressor.

[oragex]

The compressor itself rarely goes bad, but the bearing inside its pulley gets dry after 120k miles or so

The pulley on your compressor sounds dry. A nice time to also re-shim the clutch (check out the tips in the video). I also hear a second chirping sound maybe from another pulley, such as the tensioner (make sure not to put some cheap tensioner in there, better go with a used original one that has a smooth running pulley on it)

Easy check as above, with the belt out, spin by hand those pulleys, see which is dry or even has play on it