Bearing wear?
 

When I was replacing my belt I noticed on the underside a shiny substance built up in the grooves. Is this a sign of bearing wear?
Should I worry about this?

If it is a problem that should be taken care of please tell me what to do.

Thanks

Sounds like common belt wear to me. The friction on the back side from tiny changes endured with accessories engaging and the normal path of wear on the belt's surface.