I actually clean my cage every day. Thanks for the advice on the fleece!I use fleece for my boys. I haven't had any issues because, although they used to chew holes through it and tear it up, they never ingested any of it. That is to say, I personally never had any issues with fleece. If you do notice that your guys seem to be ingesting any of it, that would likely be a concern! But, in my experience, your typical, healthy rat won't eat anything that isn't edible (for example, they chew on wood chews but never consume it). That is, I wouldn't worry too much. I'd wait for some more expert opinions (I still consider myself a rat newbie), but I don't think this is something to be too concerned about.
One thing to caution you about though: if you're using just fleece, you need to clean your cage out more often!
If you're still concerned,a safe alternative would be a paper bedding (like Carefresh) -- this is something I also considered for my boys and my former roommate uses it for her pet mouse. I've also heard of some people using aspen but I think that may be something still a little controversial/debated -- wood bedding in general, that is. Whatever you use, make sure it's low dust, unscented, and nontoxic!
You are right. When things get holes in them they can become dangerous and rats can manage to get caught/trapped in the holesOk, so I have fleece lining Rinky & Bingo's shelves because it was suggested. Problem is they nibble on it & put holes thru it. Doesn't sound safe, is it? If not, what else can I use