04 5AT, 112k miles...

Just bought this car, lovin' it. Searched for my exact issue and I haven't found it... most loose bolt/flange/gasket issues go away when the car is good and hot due to metal expanding etc, but mine only shows up when it's hot...

Not sure it's even exhaust, but it sure sounds like exhaust... I get a rattle or vibration coming from the drivers side front. Plenty of "only's" coming up:

Only happens when the car has been running for 15 min, at least... has to be nice and warm.

Only happens from dead stop through mid-to low upper range of first gear (not sure if this is an RPM thing or a speed thing?) Sound goes away, for the most part, at upper part of first and through all other gears. This could be my perception though.

Only happens while car is in gear, does not rattle/vibrate in park or n

Does not seem to affect performance that I can tell.

It sure sounds and feels like an open header V8 when it happens... that low growl with a bit of vibration in the floor.

I've had a few "mechanics" (notice the quotes... just dudes, really) take a quick look/listen and I've gotten various "it might be..." from cracked exhaust manifold (wouldn't this be present at all times?), to a bad drivers side wheel bearing (again, wouldn't it present at all times with a whine, increasing with speed?), to a bad clutch fan. (That one stumps me).

Thoughts?