I just bought a 1990 LS400 and I noticed that on the highway, at around 55 mph when giving the car a little gas, the car makes a faint humming noise which sounds like it's coming from the back. The rear differential was just replaced about a week ago. The noise goes away if you go any faster or slower. If anyone has any ideas, let me know. Thanks.

-Rob

 

That's a hard call without hearing it myself. Was diff new or rebuilt?

 

I believe it was rebuilt.

 

got same noise..i suspect wheel bearing since it is only my left side and it goes away when i press on gas...