A few months ago I bought an 07 G35S, I test drove it beforehand and everything felt good. A few weeks after purchase I began to notice a certain sound that, as best as I can describe it, sounds like a hollow ball rattling in a small space. I had the dealer check it, they couldn't hear anything but said that the car is in great condition and if its a rattle it will probably get worse overtime and become easier to pinpoint.

My problem is, I can reproduce it very easily and hear it so clearly that I sometimes do it subconsciously and its annoying the **** out of me. It SEEMS to have gotten a bit louder over the past few months but my girlfriend says its the same as when she first noticed it.

It occurs when I'm light on the throttle or when the car keeps the throttle open sometimes, it goes away completely when I'm not on the gas at all. From what I can tell it gets faster with vehicle speed and seems to go away at higher RPMs. It seems louder in the back seat, directly behind the driver. Here is a soundclip of a few instances that I managed to catch it.

http://soundcloud.com/weirdg35sound/...5sound/s-y9DB7

 

I can hear something like you describe, especially at about 30seconds into the sound clip. I don't know what it is either but have you had the exhaust system inspected?

 

All I can think of is Tire or wheel related. does it only do it on certain roads or at certains speeds? Is it coming from a certain area(left front). You can try rotating your tires. Could be ball joint or something. It is hard to tell without being there. Take it somewhere else for a second opinion, if possible

 

As rpm stated, it sounds like its coming from the exhaust dude. might what to check that out. other than that, the issue could be located some where else.

 

It is clearly audible on smooth new pavement when at lower speeds (20-30mph) so that outside wind noise and such doesn't drown it out. When I'm just barely on the throttle keeping it very steady so that the engine is quiet, I can hear it the loudest. As soon as I take my foot off the accelerator, the rattle slows down a little and disappears.

I keep thinking its the exhaust as well and have been meaning to do a few drive by's with someone outside listening for it. I'm going to try and setup my laptop with a good mic this weekend and see if I can pick it up any better.

 

If it doesn't change pitch/speed when you speed up or slow down, then I dosen't sound like a wheel/drivetrain problem. Keep us posted as this is one of those mysteries

 

Does it do it when you are parked with the engine running and you rev it to the same rpms that it occurs at while driving?

Does it only do it when it's in gear? (ie can you make the sound while rolling and revving the engine in neutral)

Another troubleshooting possibility is to put your car up SAFELY** on some jack stands and "drive it" in place. This can sometimes make it far easier to identify repeatable drive-train noises.

I can recall a similar noise on another type of vehicle when the catalytic converter was going bad. Some of the ceramic honeycomb came loose within the cat housing and would rattle at certain rpms.

Good luck and don't forget to update us with whatever you find.



** If you don't know how to achieve this, then don't even bother trying it!

 

I think he said it does: