To me it sounds like he's trying to tell you something. Most likely he has an infection or is blocking up with crystals.

Fister blocked up several times and was flushed throgh 3 times at the vet, 2-3 months apart, and we kept him on Hills S/D as the vet suggested. He still blocked up - OK, not as quite as bad, but still. The vet told us that he was not allowed one single shrimp!

Well, in the end we had him operated. If you do a search, you'll find the threads about the problem and how we handled it. Boots, (Cinder & Smoke's) also had this operation. Sasvermont posted some very good links too.

All the best of luck finding a solution, and scritchies to Allen.