Heres a couple of simple checks first.
TPS Voltage The TPS can do strange things.
Fuel pressure.
Try going 40 mph in different gears. See what speed it makes the noises. Then put the car in 2nd gear and go 40. If the noise is at 40 no matter what the gear, its probably in the driveline, wheels, front or back, rearend, driveshaft. If the noise comes in either gear but different speeds, its motor tranny related. This will give you a place to start looking.