04 Rough Idle in Drive

I bought a used 04 TB, 4.2L, 2wd, w/ 46k miles on it. It runs fine but in drive with the brakes on it vibrates and I hear a low frequency rumble. The vibration and noise goes away as soon as the truck moves. Any ideas?

Tough to help with this sitting at our desks, possible exhaust grounding, engine miss at idle some rotating component on the engine noisey, someone has to check this onsite.

Based on the lack of replies it appears this is not a chronic problem.

More info: The idle rumble does not happen in Park only in Drive with the brakes on. It seems to get louder a few seconds after stopping.

The problem was the engine mounts. Replaced them and it purrs. Rough idle is gone.

Thanks for posting back, but what was wrong with them?

I don't know the specifics. The dealer (not GM) I bought it from could not determine the problem. They sent it to the local Chevy dealer. They diagnosed it as broken engine mounts. I was a little skeptical but they were right. They replaced both of them today and the rumble & vibration is gone.

I 've never seen or heard of this, if it were me I would be suspicious of this truck's backround, not to be an alarmist though.

Now you have me worried. I do know this TB was in a fender bender that got the front right. It was fixed professionally. My mechanic inspected the car before I bought it. All he found was that it needed a front-end alignment. It was a local one-owner.

If the broken mount is a sign of bigger problems, what should I look for?

How did it break, this is not a normal interval or maintenance item, something occurred to cause this, they are just not made in such a way that this fails., maybe in 15 years. I'd ask for the old one or get someone, maybe in a body shop, to closely at the frame and under chasssis.