Crepitus was my vote as well. Ask your doc about getting some glucosamine and chondroiten (spelling?). It is supposed to build back cartiledge. My knees have it really bad from all the weight they have to carry. There are all kinds of over the counter stuff with G&C in it. If you try it, make sure you give it time, it takes 6 weeks to notice the effects, but it is a long term fix. Could help you out alot, especially if yours aren't too damaged at this point...with no pain yet, i am thinking you could really benifit from some pre-emptive therapy, like the G&C.
I may not be able to lose 100 pounds, but I can lose 10 pounds 10 times!