It's been a while. My '87 203k 325ic had been behaving pretty well until I recently noticed a loud purring "woowooowowowo" in first and second gear above 3,000rpm mainly after I've been driving for a bit. I thought it might be the bearings or the diff but since it's not present in third gear, I'm thinking it's the tranny. Would you guys agree ? And is there anything I can do ?