As the topic says. The car hums and I can feel a slight vibration when letting go of the gas pedal. If I meet up with the gas pedal to the cars speed everything is fine but when kind of "motor breaking" (It's an auto) the slight noise begins. Noticeable from like 40 mph and increasing the faster I go (when letting OFF the gas pedal)

What could it be?

 

Sounds like loose pinion bearings. In that situation, the drive shaft is solidly held in place against the pinion's head bearing (big one next to the pinion gear head) when the drive train is in "drive" mode, against the "tail" bearing (small one right behind the nut) when in "coast" mode, but free to move around a bit when in "float" mode. You could try replacing the U-joints in the drive shaft as well, they can let something similar happen, but usually if they're bad, there will be other signs besides just that noise.

 

Thank you. Are the pinion bearing pressed in and the whole damn thing (rear axle) has to come out? I will check the u-joints and see if I notice any play.

 

Yes.

Not necessarily, but it's MUCH easier that way. Laying up under a car and trying to do all that work laying on your back is about the farthest thing from "fun" I can imagine. Now, if you have a lift that's high enough you can walk under it, or a pit you can stand in to park the car over, that is a different matter.

 

Hmm. Im hoping It's not the pinion bearing (I just have a floor jack like most of us). If that's the case I might as well find a 4th gen rear and work on that on the side.

Actually, the hum while coasting comes and goes. It's barely audible but my ears are sensitive to that stuff. Definitely noticeable when accelerating and then letting off.

Fingers crossed it's the u-joints. The car is mostly stock and lives a life of cruising. No burnouts. 68k miles on the meter

 

Almost certainly a cruise side issue with the rear differential. When driven under power, the pinion acts on the drive side of the ring gear and is forced forward into the main pinion bearing whereas when coasting, the ring is driving the pinion which forces it rearward onto the input bearing. Generally when you get a whine on the cruise side it's time to replace all the differential bearings, not just the pinion bearings. Pull the whole rear axle out and rebuild it, easily done with a jack and Jack stands. I have pulled the whole axle out a few times and it takes less than a couple hours to remove the entire assembly.

 

Rebuilding the whole thing might be the weekend fun for autumn and winter 25/26. I'll check the easy stuff first (u joints and pinion nut). It's just strange it would give up this early in its life. Half way, imho. Of course - I have no idea what happened to it before I laid my hands on her three years ago.