I would think fliters.
Try this. Take a piece of toilet paper, fold it up then tape it over the filter with medical tape, use ALOT of tape. then see if you can still smell the smell. And also, if it does have a problem, there will be tinytraces of poo on there.
When my filters start to fail, or turn black if id ont want to change i do that, lol. Had never had a problem until a little while ago, and i kept smelling something,and my tape had come loose! so i decided jsut to change
UC for 8 years, before finally kicking its butt and having a permanent ileostomy April 17 2007!
-I have gone to find myself, if i get back before i return, keep me here-