I'm having issues with a bad grinding sound on deceleration, mainly betweek 2500-4000 rpms. I did some investigating last night because I was certain the sound was still from the rear. I ended up hearing this sound where the rear diff connects to the driveshaft.
Here's a video: Grinding WRX Sounds - YouTube
Now here's the kicker. I'm 100% sure its not the rear differential. Why?
1. I was having the same issue before and it was recommended that I replace the rear differential.
2004 WRX Rear Differential Sound - NASIOC
2. I bought a used one from a vendor who tested it and said it was in perfect working condition. The sound didn't disappear.
3. I put my old differential on another WRX and the sound was nonexistent.
My thoughts are the driveshaft. Would it make this sound if it's damaged (only at 2500-4500 RPM)? If not, what else could it be?
Another thought.....the sound only happens in gear. If it truly is the driveshaft, wouldn't I hear it when I am coasting in neutral?
Maybe the connection between the tranny and driveshaft is bad? Is there a bearing or something on the other end of the driveshaft that could be bad and causing a sound that's resonating through the driveshaft to where it connects to the rear differential?
Funny thing is though, that there's no sound coming from under the transmission or driveshaft towards the front of the car.