I HAD the same rattle, I THINK, I was freaking for days, had the Gfriend driving the deal hitting bumps and rough roads but it would only do it under acceleration OR hard braking, on DAY THREE I found the problem, IT WAS THE READING GLASSES IN THE OVERHEAD STORAGE COMPARTMENT ,,,,WHEW,,,,,,Well I hope this is your deal,,,,,
Good Luck, oops other than that me Hummer is tighter than a ducks @$$,
.......
<font color=Gray>Pewter</font>, Lux, No Spare Anywhere
, Ventvisors,
Corsa Touring Exhaust,
HID's