puzzling creak trouble shooting
I have a small Giant Rincon budget mountain bike that my sister rides when visiting. I bought it used for cheap ($10). The bottom bracket was shot. The shifters shot. Most everything in bad shape but it did brake (mechanical disc brakes) and the wheels seem fine and true. For is just a spring fork, ugly but works. So, I took used parts to rebuilt the drivetrain. When I rode it, it had a puzzling creak that would come and go when pedaling. It felt like the bottom bracket and there was evidence that the bb was at one time partially cross threaded. I did try a different bottom bracket and different crankset and it made no difference. I brought it in to our local bike coop and they retapped the bb shell and checked the frame to see if it was bent. Frame straight. Replaced the threaded bb and no change. Still creaks.
Other suggestions? It seems as if there was enough threads to hold the bb tight but it is odd to screw in, one person has to hold the axle level so it screws in straight.
If in fact it still is the bb any suggestions? Or toss the cheap frame and start all over?