Okay, so here's the description:

- Hum/moan type sound from rear end. Kind of sounds like a swarm of bees caught in a coffee can.
- Doesn't change pitch or volume with changing speed.
- I hear it mostly over my left shoulder.
- Starts around 25 mph. Constant after that.
- No change on acceleration or deceleration.

Any suggestions? I'm just as interested to know what it CAN'T be. Tranny? Differential? Tire Noise? Wheel Bearing? Exhaust? If anyone can rule anything out I'd be grateful. It's driving me freaking nuts. It's going in on the 30th.

 

If it doesn't change pitch or volume with changes in speed or acceleration, my first guess would be a vibration being caused by something like your exhaust system, or a heat shield, maybe?

Anything that rotates that is causing noise will usually change pitch or volume with changes in rotational velocity.

Or possibly an electric fuel pump.

HAVE YOU LOOKED UNDER YOUR CAR TO MAKE SURE THAT THERE ISN'T A BIG PIECE OF DUCT TAPE STUCK UNDERNEATH YOUR CAR, OR A PLASTIC GARBAGE BAG, OR SOMETHING- TAKE A LOOK AROUND!!

 

I had bad pinion and carrier bearings in my Lincoln LS that had a bad moan from 25 mph up. It didn't really change pitch either. Sounded VERY bad though. Gears were fine.