Since it's gotten cold here, I have noticed a weird sound coming from what seems to be the rear of the engine or could be the auto trans or t-case. The best I can describe it is as a fluttering sound, only happens from about 2500 to 3100 RPM. It usually goes away after it's good and warm, but I notice it sometimes even after that, although it is fainter. Doesn't sound like a valve or anything to me. It does it in every gear, including neutral. I took my brother for a ride (he's a mechanic) and he wasn't sure what it was, but said not to worry about it. I drive her anywhere from 600 - 1000 plus miles a week for work, so I want to make sure everything is cool. Any ideas?

 

If I would have to guess I would say exhaust leak.
May be some else will pith in.

 

What he said. maybe a crack in the manifold or pinhole that seals up when the material gets warm and expands, or even a bad gasket. aslo sometimes a sticky egr valve will make a similiar noise

 

I'll have to check out both, thanks for the suggestions.

 

That would be the chipmunks....