I think you need to do some detective work...find out what part of the machine the noise is coming from. A thud, or popping when the needle goes down can just be a dull needle..a racket under the bed can be a dirty bobbin area, or even just a stray thread caught in there. A whining up by the top can be threads caught somewhere..anywhere!
Listen to it when it's running, then just turn the handwheel and see if you can duplicate the same sound.
I had a very quiet squeak on my machine every time the needle went down..drove me insane! I was sure I was wearing out some part that couldn't be replaced...finally found the offending area and oiled it, and now it's great.
Don't give up on your machine...just spend some time looking for the issue..eventually you will find it!