i have an 01 2.5 rs. minor mods. intake, cat-back brullen exhaust, sti suspension, 17" rims.

in 4th gear at 50 mph there is a ... hmm... how do i describe this sound... whoo...whoo....whoo...whoo... it dosent get faster or slower with speed, and goes away when i shift to 5th ?? its hard to hear over the exhaust, but there is definatly a noise.

ive thought it might be wheel bearings, or brake rotor. but im not sure. of course i brought it to the dealer and they didnt hear it.... big surprise...

any help would be greatly appreciated.
p.s. i have 33,000 mi

thanks,
-adam