Well it could be anything, most likely they were not coded good, and ended up in bad quality. If you have a low spec comp. 400 Mhz integrated 8mb vid card, and stuff around that area, then the comp might be messing up. But then agian it just might be the file, try downloading a different version of that episode from diff fansubs.

ANBU & Aone
Bakasan
Scarywater
ect.