Loud noise under hood

frustrated · Post by **frustrated** » 12 May 2017, 13:39

I have an 07 xc90 3.2. There is a very loud noise coming from under the hood. Noise is there hot or cold and gets louder while driving. I replaced the belt tensioner and idler pulley a couple of months ago because I thought that's what the noise was. Noise still present after I replaced those parts. I took serp belt off and started engine and noise goes away. Ac comp checks out ok. Ps pump seems fine also. Everything that moves with the belt is ok. I thought it may have something to do with the alternator but it still spins when belt is off so that eliminates that also. Any suggestions???

traudesa · Post by **traudesa** » 12 May 2017, 14:01

Even if they spin freely, one of the belt-driven accessories could still be the problem. I remember that when the bearings in my wife's alternator went out it sounded like an air raid siren but still spun fairly well. Based on your description, anything that gets spun by the belt is suspect. I would get a mechanic's stethescope (listening to the end of a long screwdriver will also work) and start probing each of the accessories while the engine's running. Be careful of the belt, naturally. That will let you hear exactly what's going on in each component and pinpoint the noise. Probe everything, even the tensioner pulley, so you can objectively rule them out.

Let us know what you find!

frustrated · Post by **frustrated** » 04 Jul 2017, 14:54

I used a stethoscope and probed around all the moving parts. The noise appeared to be coming from the ac comp. So I ordered one and changed it out,only to have the same exact noise. I returned it and put another one on..still has the same noise. I don't see three ac compressors making the same exact noise. I removed the alternator to check the coupling and the bolt that attaches the drive gear to the pulley that drives the serp belt. All appears to be ok. The noise is extremely loud at the ac compressor, like something is going to fly apart loud. But like I said after three of them and still the same sound I have my doubts.

Post by **June** » 04 Jul 2017, 15:12

Isn't there a chain drive on the rear of the 3.2 that runs the compressor?

frustrated · Post by **frustrated** » 04 Jul 2017, 15:28

No the serpentine belt runs it. I'm not sure about a chain drive but something drives the alternator and the serpentine belt from inside the cover. That's why I removed the alternator to check the coupling and the bolt for the pulley that drives the serpentine belt

Post by **June** » 04 Jul 2017, 16:19

There is R.E.A.D. at the back of the 3.2 that runs belt driven items that is powered by the timing chain. At least on the S80 3.2. It was one of the things that I did not like about that engine. I think R.E.A.D. stands for rear engine accessories drive. It's been a while since it was explained to me but might be your noise as I have heard they go bad. June

Post by **oragex** » 04 Jul 2017, 16:51

Can you upload a video on Youtube, that would help us better understand the kind on noise. Have you refilled with refrigerant and the correct amount of oil the a/c system?

frustrated · Post by **frustrated** » 04 Jul 2017, 18:41

The compressor was supposed to have oil already in it. I assume it has the right amount

Post by **ALF1** » 17 Jul 2017, 15:05

Check the pulley on the alternator shaft. It's one of those that guide the serpentine belt. My 2003 XC90 AWD 2.5T had a noise in the engine compartment at 210,000 miles that I could not identify. Got louder and louder. I finally noticed the serpentine belt pulley on the alternator started to float axially in and out. Drove home carefully, but not in time....the pulley came off and the serpentine belt fell off. Drove home under battery only and eventually a tow. The alternator pulley bolt had loosened and then the imbalance ground off the threads on the alternator shaft. The pulley is threaded onto the alternator shaft and then bolted on. I didn't notice the bolt or its loosening because they put a plastic cover over the bolt head. I suggest that you pry off the plastic cover on the end of the alternator pulley and tighten the bolt. If it needs a lot of tightening, you may want to remove it and inspect the shaft threads.