my 1999 3100 53K Miles has a knock that is not in sync with the engine rotation, and speeds up from idle to about 2000 rpm, then it dissapears when accelerated further. At all speeds it is not in sync with engine rotation. It also is not always there. Iw will be there for 30 minutes then gone for days. I cant find answers. Is there any websites that would have soundclips that I could listen to, to help me identify it? I am lost. I posted here before and really didn't get many answers so I am trying again. Thanks