My mechanic friend who I completely trust with my car, recently changed my: upper/lower intake manifold gaskets, fuel pressure regulators, valve cover gaskets, and some other minor stuff. The car runs perfectly fine and is as smooth as ever. Only thing is that after driving her for a bit and I come to a complete stop, there is this vibrating noise, it gets pretty loud. It isn't the brakes, it sounds like its coming from the center console or something. But once I begin to press on the gas the noise disappears completely. I can only hear the noise when I come to a near complete stop and when I am stopped. Other than that, it's as quiet as ever. Something also to mention is that when I start the car up, there is a sound that comes from the center console, sounds like something is shifting in there? It sounds like its coming right behind the 6 disc cd changer, its super quiet but I can definitely hear it. My check engine light came on about 3 weeks ago, code P0440 and my mechanic said it was most likely a leak from when he was doing all that work under my hood, he cleared it and it hasn't popped up again since. I don't want to take it into a shop and they go looking and charging me for stuff that doesn't need to be replaced. I will try to get an audio clip of the noise so maybe someone can better help me diagnose it. Any help or input is appreciated guys. Happy New Years!

 

Plastic vibrating most likely. Your 3 motor mounts most likely need replacing.

 

If you have the possibility to take it up on a hoist and check with the engine running. Can your mechanic listen with a stetoscope?

 

I know mines need replacing, this is what I was thinking it might be. It's an 02 base model LS430 with 60k miles. The noise only happens in drive and reverse, when in park or neutral the sound mostly disappears. Is there any way I can further diagnose it to make sure it is indeed the motor mounts? She drives fine so I am guessing that for the time being it is alright to continue to drive her, but should I get them replaced ASAP? Thanks for the help.

 

First you need to inspect the mounts. If the mounts need replaced and if it bothers you then replace the motor mounts.
If it doesn't bother you then don't replace them.

 

It becomes a matter of eliminating problem areas. If you say it occurs when in drive (forward/reverse) it is related to the driveline - directly or indirectly.
If you can, take it up on a hoist and inspect from below. The mounts are there to separate vibrations from the engine to body. If you can inspect them from below it might already give you an indication. If it is not the mounts, I would check the driveshaft - is there play? Turn the driveshaft by hand and listen if there is noise in the transmission.
If you decide it is in the dashboard (loose wire or some plastic material not tight) it becomes a matter of money. Should you open the dashboard or not.
In any case report back what you found