Engine rattle

[jsrnsis]

I've tried searching for threads with similar symptoms and ruling out everything I can think of, but I just can't seem to figure it out.

I have a 98 v70xc, 178k miles, relatively recently rebuilt head. When the engine is around 1500rpm, I get a strange rattle that seems to be coming from the backside of the engine, though I'm not entirely sure. At idle there is a similar noise, but it really starts at around 1500rpm, no matter if the car is in park, drive, or reverse, and then disappears over around 2000rpm. Its a metallic, rattily, groaning sound.
I checked all the mounts, I had already replaced the firewall bushing and passenger side mount under the crank, but the front hydraulic mount and odd AWD drivers side rear mount seemed fine, just old. I got under the car and the heat shield around the cat seems solidly mounted. The heat shield over the turbo is also nice and tight.

Noise can be heard inside the car a bit more clearly since its not drowned out by the rest of the engine, and listening with a length of pipe also leads me to the rear. My fear is it could be something turbo related.

[BlackBart]

Back (left side) of the engine for sure? Not the front and water pump or idler/tensioner?

Do you have a cheap motor stethoscope? You can hunt for the exact spot the noise is coming from.

[volvolugnut]

A loose heat shield on the back of the engine?
vpolvolugnut

[jsrnsis]

Back (left side) of the engine for sure? Not the front and water pump or idler/tensioner?

Do you have a cheap motor stethoscope? You can hunt for the exact spot the noise is coming from.

I was using a thin piece of PVC pipe as I revved the car from the throttle. It was honestly pretty hard to tell where it was coming from, but moving my head around I seemed to hear it louder at the side of the engine facing the rear of the car (left or right of the engine?)
Also intermittent relay clicking sound from the front of the car by the fan, but seems unrelated.

I'll try to see if I can get a video of it when I get home later.
I replaced the timing belt, tensioner, water pump, and idler when I had the valve stem seals replaced.

[BlackBart]

I see - the back side / firewall / exhaust side, hmm.

Turbo bearings starting to let go? A turbo impeller touching the side of the housing will make a LOT of noise.

Exhaust manifold bolt loose and rattling?

[scot850]

I would look at the heat shield as mentioned previously by volvolugnut. The metal can break around the mounting bolts. When you refitted the heat shield at the exhaust manifold, did you use the springs on the bolts?

Neil.

[jsrnsis]

I would look at the heat shield as mentioned previously by volvolugnut. The metal can break around the mounting bolts. When you refitted the heat shield at the exhaust manifold, did you use the springs on the bolts?

Neil.

Yes, springs on the bolts, all bolts tightened. I had to get new stainless bolts though, the originals were extremely corroded.
I will check more heat shields, maybe it's one further back and it's more exhaust related. The rubber hangers all the way back were stretched enough that the big heavy dual muffler AWD exhaust was able to swing far enough to melt a bit of the mudflaps at some point in the past. But this is a different rattle. I did notice some of the mounting points of the heat shield to the steel were corroded, but the ones I was tugging and prodding seemed solid.

I picked up a mechanics stethoscope (harbor freight) but it was cold and damp out today and I have to admit I just really didn't want to be crawling around under the car.

[jsrnsis]

I see - the back side / firewall / exhaust side, hmm.

Turbo bearings starting to let go? A turbo impeller touching the side of the housing will make a LOT of noise.

Exhaust manifold bolt loose and rattling?

When I had the airbox->turbo pipe out recently to get at the ABS module bolts, I tried to wiggle the turbo impeller and it seemed very solid, no play. Tomorrow is supposed to be 10°F warmer and not rainy so I'll definitely have to try to record the sound and poke around with my new mechanics stethoscope.
I also picked up their "swedish pattern" pipe wrench because I just couldn't help myself.

[jsrnsis]

You can just make out the rattle in question over the engine noise.
I'm starting to think maybe it is a heat shield?
It's a strange sound, almost groaning.

Poking around with the stethoscope:
Power steering pump/serpentine belt area- just normal belt noise
Top of engine- happy engine sounds
Heat shield above turbo- no rattles

I then put the probe on the wastegate actuator vacuum chamber, and heard the rattle through the stethoscope as I heard it with my free ear. Just to make sure, I put the probe on the actual actuator arm, and I didn't hear the rattle through the stethoscope
It seems the vacuum chamber was just amplifying the sound.
I put the probe on what I think was the body of the turbo, again, very faint, intermittent rattle sound, it was louder with my free ear.
This just leads me to think it's something connected to the exhaust.
Is their a heat shield under the turbo? I had a hard time trying to get a look up in that area.

Or maybe someone can confirm that sound as being a heat shield or other cause, since the other volvos I've driven have their own interior rattles to cover any engine bay noises up.

[abscate]

I’m driving down from Albany later this morning, can give a listen. Pm sent.