I'll make this brief, and if it has been covered here just refer me to the existing thread.
My SNES seems to be having issues with Mode7 related stuff, namely when something is spinning and scaling at the same time. The games affected the most seem to be Pilotwings, Actraiser, Contra III and Axelay, although Pilotwings and Axelay are the only ones with gameplay related issues (the background is mostly gone in Pilotwings, no matter what stage, and any ships that have appendages made up of multiple sprites go nuts in Axelay). I have yet to check some of my other games, aside from F-Zero, which oddly has no problems that I've seen.
I've thought that it might be a dirt issue, but I figured I'd check here first. If more info is needed, I'll post it here later.