it's a good thing that the vet didn't find anything medically wrong
with him...now you need to play detective...get on your hands and knees
and literally follow him around...he may be rubbing on something...one
of his cage mates may be doing this...it could be anything...but you'd
be surprised the contortionists they are...this could be something very
simple...

i had a ferret that kept getting sores on his hip, just one... after
alot of tests, i found out that he used the bottom of my couch to rub
against almost like a bear with a tree...once they lose the fur, it
itches when it has to grow back in, then they rub or scratch more,
hence the cycle begins!! you can actually put a bit of lipstick on the
spots to see where it ends up...a bit won't hurt them, but will tell
you quickly who's nose it's on, (or not), or what object,,,..but check
everything!!

good luck, let us know!

[Posted in FML 5442]