There are a couple threads on this subject in the JR tech forum. I have these servo's too, and they do "chirp" a lot, but I don't get any noticable movement on the control surfaces they are assigned to unless I am in my garage around a metal bench.

Best I can remember, the folks at JR said that the chirping was the servo constantly finding center. Just as others have said, when I put a load on one (stick movement) the chirping stops and the works fine. If I move out into the yard or am at the field (i.e. not around all the metal stuff in my garage) the chirpping all but stops.

Just my .00000002 worth.