I recently received a lot of tapes and have slowly been going through them. I have encountered one brand, Reeves Soundcraft S-12 Acetate, that has been giving me problems. One or in some cases both channels don't work unless I physically add tension to the tape. They also seem to make the tension arms jump around when rewinding/fast forwarding. I looked around but couldn't find any answer. So far I have 5 tapes that do this, all those two brands. I think I'll end up dumping the tape and keeping the reels as they look cooler than the Scotch ones.