Happens when I'm sitting at a light and started about two weeks ago. A/C off, so it's not the compressor. It's not the aux fan either. I know what that sounds like.

Sitting in neutral at any given light, I hear a noise that sounds like someone throwing rocks at the underside of my car. A muted "pop" every so often. I've timed the pops with the stopwatch and they have no meter. Very random. Anybody else heard this? I thought it might be the pipes and/or cats pinging due to heat expansion, but it doesn't sound "metallic" enough for that.

Any ideas?

 

Brad-

I get the SAME noise from under my car. I just assumed it was the cat(s). The noise continues after the ignition is cut off, too, so that's why I figured it was just expanding/contracting noises. I hear it at a stoplight, etc. Do you hear the popping noise after you cut the ignition? The noise is very regular...

 

But, do you hear it eminating from different spots under the car? Yes, I've heard the cats cooling outside of the car after shutting it down and getting out. I guess it just sounds different from inside the car.

One more thing. If I expand upon the description of the sound, I'd liken it to a very tiny backfire when inside the car. Would you agree that's the sound you are hearing as well?

 

This is puzzling if its not the usual cat popping. My car idles a tad rough and sometimes softly gurgles. Occasionally I hear what I think is a VERY muffled pop that sounds like a tiny misfire, but only when I'm standing outside the car. I'd never notice otherwise. Can you elaborate any more? I never notice the sounds' source changing...

The cat noises (I assume) that my car make are so loud that I can hear it when idling with the windows closed or even at a stoplight with the windows open and people blasting music next to me.

 

You know the sound a marble-sized rock makes hitting the plastic wheel liners? That's what I'm hearing. Sometimes it's directly beneath my seat, other times it sounds like it's coming from the passenger front corner or driver's front corner.

I've had 10 cars in the last 10 years and not a one made this loud of a noise when the pipes/cats were contracting expanding.

 

I know that sound but I don't think I'm hearing that from my car. I do hear the popping of metal that HAS to be the cats, although I've never had a car that made such noises either. Its not the same noise as you're describing, but you said you get the normal metallic popping, too? How many pops does it make at a time, a single one or multiple sounds?

All I hear is what has to be the regular cat-poppping...

twang..............twang................twang............... ....

Its very regular... almost a cadence...

I really wonder what the sound you're describing could possibly be? Maybe its a tiny backfire... I dunno... Can you hear it from the exhaust tips as well?

Sorry for all the questions, but I'm just trying to see if I can help at all.

 

I just noticed the popping noise after engine shut off today. I sat in the garage for 5 minutes and it decreased but kept on popping.

 

https://my350z.com/forum/showthread....t=cats+cooling

I believe it is just the exhaust cooling down (the noise is the metal contracting). It is completely normal.

 

I had them too, so I actually stuck my head under the car somehow to check it out... the noises I am hearing is the A/C fluid dripping down onto the exhaust pipe under the passenger seat... when the liquid hits the exhaust, it sizzles, making the popping noises... took it to a dealer just to make sure, and he confirmed thats what it was... every 10 seconds or so it happens... hope this helps!