I have a thumping sound coming from the undercarriage of my 04 G35 6MT coupe while its in a stand still not being driven just on, idle good and everything any suggestions what it could be?

 

I would do a close visual inspection of all the accessory drive belts, you might have a torn piece causing the noise.

 

Thanks for the advise bro. Much appreciated.

 

No problem brother, let us know how it goes so that we can continue to help if needed.

 

I'm also getting it ready for a smog check this month I live in Cali, which sucks with all the emunission test and what not. Can't really do any major gain mods do to the star certification smog test either. Any suggestions on Cali legal mods that would pass Cali smog test. Also any good preps so my g35 will pass smog without any problems thanks for all the replies.

 

Does your idle skip at all when it thumps?

 

Not at all on a cold start it sits at 1000 to 1500 Rpms. Once warmed up between 0 and 1000 rpms.

 

Stock clutch? It's probably just the flywheel. A weird low thud sound and sometimes some chatter noise, it's odd but perfectly normal on these cars.

 

I'm talking about a very minor deviation... like when it's fully warmed up and idling at a stop-light at around 800, will it ever make the thump noise and then drop to 650 for a half a second and then bounce back to 800?... sorta like a slight misfire or hickup.

 

When were the spark plugs last changed, if at all?

 

That makes a lot of sense bro thanks. Quick question what clutch and flywheel you running.

 

Not at all bro idles fine cold or hot. I thought it was the same thing but after close attention at the idle noticed that wasn't it. But does sound like a very slight misfire.

 

Just recently changed them and the noise is still there.

 

The reason I ask is that mine kinda does that. It happens sometimes after a rip down the highway and I am sitting at the stop light at the end of the ramp idling waiting for the stop-light to change. It will do it like once every 8 or 10 seconds but not really in any reliable pattern. It doesn't affect drivability at all and doesn't seem to do it any time except when idling and mostly when the car is fully warmed up. I haven't noticed it doing it at all when the car is anything but fully warmed up. It's done it for as long as I can remember.... or at the very least for 4+ years. I only have 52K miles on my '04 6MT too.

How many miles do you have?

You should try to make a video of it doing the noise and post it up on youtube with a link to it from here.

 

Stock clutch and flywheel. It's been noisy since day 1.