Loud hum from rear

Ive lately noticed a loud hum from the rear of my 2000 323 Ci. I'd like to think it's just road noise from my winter tires, since it wasn't that loud with my summers on. I looked up some info from this forum wrt rear diff noise and I think I'm ok but I'd like to have a plan be if I'm wrong.
My question is " Can I swap out a rear diff from an M3 and if so, what years are compatible with a 2000 E46?"

Search. M3 diff swap is well documented. You're going to need a lot more than the diff to get it to work.

All jokes about noises coming from your rear end aside....I had this same problem on a 2000 323 Ci also. The mileage was around 150K and it ended up being one of the rear wheel bearings.

Simplest way to find out; Jack/Lift the car up securely on both rears and inspect the vehicle in motion with a partner.

Thanks for the advice. I'll look into the wheel bearing as a possible. The jacking up and letting 'er spin gives me the shudders. Haven't you seen Ferris Beuler's Day Off?
As far as the "Search" advice: It took you longer to type that than a simple yes or no.

When I did my wheel bearing it was the drive's side and it was a 8!tch, I had to remove the trailing arm and take it to a shop to have the half shaft pressed out. I also did the passenger side and it was easy and did not require removal of the trailing arm. Be careful then pressing in the bearings...you can press the middle out of the bearing and ruin it.....yes it happened to me. Also....do the fronts too. You have to buy a new hub with bearing for that one.

If the sound gets louder as you accelerate and lower as you slow down its most likely your wheel bearings, I had the same problem and new ones took care of the noise, my 2 cents...

I diagnosed a bad wheel bearing by doing a slalom while driving. Try to see if you can make it better or worse by swerving wide while doing about 30mph. If the noise goes away or gets worse when going a certain direction you are one step closer to a solution. GL

Originally Posted by HerbicidE46

If the sound gets louder as you accelerate and lower as you slow down its most likely your wheel bearings, I had the same problem and new ones took care of the noise, my 2 cents...

The loudness is constant. Just the pitch changes (Goes higher and lower) as I accelerate or slow down. That's why I'm thinking (read hoping) it's the snow tires.

Originally Posted by willsbma

I diagnosed a bad wheel bearing by doing a slalom while driving. Try to see if you can make it better or worse by swerving wide while doing about 30mph. If the noise goes away or gets worse when going a certain direction you are one step closer to a solution. GL

Good idea but in the snow, I'm pretty much hooped. parking lots are packed snow around here for much of the winter.

Didn't realize you were snowed in, sorry. Id just jack up each wheel and see which one is wobbly or sounds funny

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Prob wheel bearing, at 50 and 74 mph I can hear a definite hum from the rear. Gonna replace it at some point when I get the tools to do it. I don't have a good torque wrench or breaker bar or anything.

What would it cost (including parts) to have an indi fix it?