If you can't find the culprit, there is always a chance something came loose internally in the head unit. In which case a used head unit might be in order (fairly cheap) or it might be time to consider an aftermarket (or Scion) "upgrade" (cheap----to----expensive).
When pulling the trim off, theres a write-up here somewhere, try not to rush yourself to much. Make sure you logically think about what and where your pulling, make sure you've gotten all the fasteners out, and try not to destroy the trim piece. (it does take a little force though, so don't be to timid.)
Good Luck to you, and welcome to the forum.