Noise Under The Hood

Maintenance/Repairs
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1

When accelerating, there is a noise that sounds like it is coming from low down in the engine compartment on the passenger side. Difficult to describe but it seems to be in sync with the rate of acceleration. It disappears when “cruising speed” is reached and I can’t hear it if I rev up the engine while standing still in Park or in Neutral.

2

I Don’t Think “Noise” Is Going To Get It. Can You Use Words Like Pinging, “Tink, Tink, Tink, Tink” . . . , Or Describe It As A Growl, Screech, Rattle, Clunk, Etcetera ?

Can you relate the noise to some other noise ? Does it sound like a Mourning Dove or shaking a can with a marble in it, for example.

We need more to go on here.

Thanks,
CSA

3

Hi CSA,

It is not pinging, or Mourning dove, maybe somewhat like shaking a can with marbles in it. It is a little like a metallic growl or, even, a rattling sound but not a clunk. An android manufactured completely of tin giving somebody the raspberry with his tin tongue over his tin lips might make a similar sound. I will, also, listen some more to see if I can come up with another description or more. I don’t want to make an unwarranted assumption but the phrase, “exhaust manifold problem” comes to mind but then there is the matter of no noise when increasing revs while parked.

Thank you, Rod

Rod

4

It is very likely to be a loose or bent heat shield on the exhaust system.
Putting the car up on a lift should help to confirm whether it is a loose or bent heat shield.

5

Hi, again, CSA,

I did some more listening and when starting up between two cars in a parking lot between two cars with my windows down, I could hear that noise. When I got home, I listened in my garage with the windows down and the accelerator pushed down quite far and I heard the noise again so it does happen when the car is standing still with higher than cruising RPM.

6

Hi CSA,

That sounds like a pretty darn good diagnosis. I will take the beast to my independent garage guy who does good service and have him take a look.

Thanks,

Rod

7

Sorry, VDC driver, I called you CSA. I think I need new glasses.

Rod

8

This is consistent with many instances of heat shield problems.

9

Rod, What Is The Model-Year Of This Volvo 850 And Do You Know Which Engine It Has ?

You might as well tell the approximate number of miles on it and tell us whether it’s got automatic or manual transmission.

With that information I / we can possibly help more. Some problems are more likely to be vehicle year / model / engine / miles specifc.

CSA

10

The heat shield everyone is alluding to is just a stamped piece of metal typically spot welded or tacck welded to the corners of the catalytic converter. The spot or tack welds rust through and the heat shield rattles at a specific resonant frequency. The accepted and permanent “fix” is to wrap a long worm-type hose clamp around the shield to secure it. I’ve used this fix myself.

Loved your description, by the way. Priceless.