Hi guys, hope all are well. Itís been a long time since I posted here. I guess that's partly due to the bullet-proof nature of the WRX... I really havenít had any issues. Until now.

Short version:
How hot should the rear differential get after a 30-minute highway ride (~65mph)? Should it be so hot that I canít touch it, or should I be able to rest my hand on it and enjoy the warmth it offers?
2003 WRX, stock (no modifications)
180,000 miles
80F ambient temp
Oil checked in diff and confirmed to be at correct level

Longer story:
Thereís a significant whining/whirring sound coming from the rear of the car that was barely-noticeable about a week ago. I had my buddy ride with me and crawl around the inside to confirm that itís coming from the rear differential area. It gets progressively faster as the car moves faster, and I can even hear it as I come to a stop (down to ~10 mph) when it sounds like a soft grind or rub. The sound is unaffected by gear selection or brake application, and the only effect that accel/decel has is to speed-up/slow-down the frequency of the sound. It gets more-pronounced as it gets warmer, too.

I (stopped first) got under and touched both rear brake backing plates and calipers and neither of them are hot. Sure, they are warmer than ambient, but thatís about it. However, the rear diff is hot as hell. I canít keep my hand on it after my 30-minute @ 50mph average (max ~ 70 mph) commute... itís freaking hot. Should it get that hot?

So I mentioned that I had my buddy ride around w/ me, and we were only gone about 8 minutes at average speed of ~45mph. When we got back, I asked him to feel my rear end and tell me how hot he thought it was. He did and reported that while it was warm, it wasnít as hot as I had described it . He went on to say that he found the left side of the ham was warmer than the right. I crawled under there to confirm and found that it was indeed slightly hotter on the left, and was overall cooler than in my previous temperature-sampling event. From this data, and the sounds he heard while performing the ride, crawl, and listen session he concluded that it was a bearing and not the gears making the noise at the rear diff. I plan to lift and crawl under the car over the weekend for a better inspection.

What do you guys think is going on and should my rear be so hot and bothered?