intermittant muted popping sound under hood

mazenblue · Post by **mazenblue** » 12 Apr 2017, 19:11

I have a 1998 S70. I am experiencing a muted popping sound that comes and goes and which seems to be coming from under the hood . I haven't been able to pin point the source. Sounds louder when I stick my head under the car.

Sounds like a pressure relief valve or some such thing. It is rythmic and at a frequency similar to RPM. Hard to tell if it goes up with RPM as I cant hear it in the car.

I did a PCV test (no fumes from dip stick, glove on oil fill hole did not inflate). Does not sound like the Utube squeal associated with EGR valve.
No apparent related issues, just a funky sound that comes and goes.

Any ideas?
Thank you
Maze

Post by **theWIFES_S70** » 12 Apr 2017, 21:14

Maze, does it proceed a P0455 or P0442 check engine light sometimes?

We've had the same sound for about 2 years now. I believe it might be related to the air pump or something connected to the air pump? I haven't been able to figure it out...

I wonder if it's the airbox thermostat... I plan on deleting the airbox thermostat this weekend I'll let you know if that gets rid of the sound. It doesn't seem to happen on our car when we're idling...

I don't think it's that's vital for the car... So I really wouldn't worry about it too much.