I have a incredibly loud rattle (sounds like rocks in a cooking pan) coming out from under my car only when Its cold. As soon as it warms up it stops. but it does come and go while warming up. I have no cats and I have full open exhaust so Its not the cats rattling. I did have it up on ramps this weekend but could not pinpoint where it was coming from because my car is lowered also. 08' Coupe/5AT 100k on the odometer. Any ideas! Thanks

 

Heat shields around the exhaust? Have you out it up on Jack's and given things underneath a wiggle?

 

Maybe valve clatter? Not familiar with the VQ35.

 

best to jack it up and start it up cold and listen.

 

Yeah take a look under your car when making the sound put your hands on things and apply pressure feel for anything loose you will know when you find it as the sound will stop.
Same thing was happening to me when I first got my car was killing me especially idling at a red light or going through a Drive through OMG could not stand the noise. Turned out to be that the heat shield around the cat had gotten pretty rusty and were rattling again the cat. Well ripped those ****ers off and problem solved.

 

As Op mentioned that his cats are off the car....I'd suggest that he check the harmonic dampers....especially the one at the end of the 5A/T ...its made up of a bunch of stacked metal plates with a bolt thought it ...a couple of the plates came loose on my 5A/T a long time ago and it used rattle the way you have described....(I put some RTV between the loose plates and it solved the problem)

from what I could tell they put more of these dampers on the early versions of these cars to smooth out the operation until they tuned them better or something on later years as the newer ones don't seem to have as many... that little b***h on the 5 A/T drove me crazy for a while...good luck Op

 

i had this weird rattle i could hear when i drive next to park cars or a wall. it sounded like a wind up toy. my friend figured it out for me while my car was on his lift and he heard it. turned out to be an exhaust leak. so the defective gasket was changed out and no more rattle sound. i didnt even know an exhaust leak could sound like that. my friend was surprised too. i actually thought it was coming from the front of the car. ended up the sound was coming from the gasket in the rear seat area of the exhaust lol

 

Ha complety missed that sentence for some reason.

 

the factory exhaust has a tendency to have baffles separate inside the can. Mine does the same thing. Try hitting the muffler with the car off. If you hear a similar rattle, there's your issue.

 

This! On my previous car, a Mustang, the bolts connecting the headers to the H pipe were loose and sounded like I was dragging metal under the car. Replaced the gasket and tightened the bolts and it fixed the sound. You would never guess it was an exhaust leak from the sound of it.