Remember putting cards on your bicycle spokes to create noise?. Thats what I have between 20 and 40 mph. Noise goes away after 40. It was time for shocks and brakes. I've replaced the shocks and the brakes. Everything is within limits. New water pump and belt too. The noise is still there. I have michelin pilots for the tires. 1993 Sc400 with 165,00 miles. I've managed to fix everything else from this forum. Thanks in advance....Jane

Check the drive shaft center support bearing. It is encapsulated in rubber and will deteriorate with age.

Good luck.

Is it coming from the front suspension? Does the noise change when you apply the brakes?

could it be from wheel bearings?

Sorry for the delay... Had to go out of town. The noise does not stop with the brakes. It is related to the speed. I'll check out the drive shaft this week. I've got acess to a lift. Doesn't sound like wheel bearings. My experience is failure at high speeds for bearing noise. Of course airplanes are different than cars.Thanks Jane