So for the past 2 months my car has been making a humming noise (I don't know how else to describe it). It seems to be coming from right in front of the passenger seat. Today I replaced the passenger side half shaft and have done the wheel bearing. This noise gets louder as the car gets faster what I'm saying is it follows what the wheels are doing not my tach. Now as I was putting the half shaft back in today I spun it and was hearing a noise that was coming from the transmission. This was similar to the noise that I had been hearing while at speed. What I am wondering is has anyone else had this issue or heard of this and what could be causing this is there some bearing in there that could be shot that needs to be replaced? I anyone can help me out that would be great.

 

It sounds like I am having the same problem. I have 181k on my 2001 malibu, and started hearing a howling noise about 1000 miles ago, at first I thought it was tire wear, but found out as it progressively got louder that the noise is most likely coming from the transmission. I'm guessing it's a bad bearing on the differential or worn gears. Did you ever find out what was causing the problem?