common problem rear?

Hey everyone!

I'm pretty new to the Vulcan "club", so I registered to this forum. Mainly because I love this bike, especially my own, but also becauseI have a problem I keep pulling my hair out with.

I got this bike from a friend for free, he knew I love his bike a lot, he bought a 2000cc Vulcan, so I got his older '94 750 for free. However it had a grinding noise when shifted in gear. It idles fine, revs up great with a little pop when i close the throttle after a short rev. but whenever I tried to put it in gear, it started grinding, and would not go in gear at all. not even on the stand with the wheel clear off the ground.

After that I started digging, and eventually found that the final drive at the rear wheel was grinding. So I replaced it with a used part, since new they're (not quite) in my budget at the moment. (new starting at about 1100 euro) . I drove the bike a few meters and everything was fine, shifted into all gears, drove really amazing, my legs were shaking of excitement.

Today, a few weeks later, I installed some new exhausts since the old ones were rusted and gone, I wanted to drive it again. So I went a few meters. about 200meters i think, and it started grinding again.. What could it be? I'm not in the position to spend 1100 euro on it at the moment.

The noise is definitely coming from past the shaft, or atleast at the rear wheel-height.

any tips I could check, replace, lube, fix?

I'm a car mechanic with a passion for bikes, so I'm quite handy with tools