some rats are just bar chewers. Our Inky, everytime she saw us, it was chew, chew, chew. She wanted out, out, out. The other rats haven't done that. Well Sox just started it once in a while after I put her in the new huge cage. I think she was stressed because she and Chops were in a new cage. I've never heard it hurting ratties, maybe our ears and nerves.
You could try adding extra toys for chewing in the cage. I do keep some blocks of wood for chewing. The boys are chewing on the parrot ladders in the cage. Hmmm one of the legs is looking kinda rough.
boys: cadoo, cosmo, jinx, moe, ziggy
girlies: sox, chops
gone: Inky--2/7/07 Oreo 4/1/07