Do you mean rear surrounds (not the normal side surrounds) as in a 7.1 system? If so, the first thing to be aware of is that they will make no noise at all if you are using a regular 5.1 track unless you engage an upmixing DSP like Dolby PLIIx. So that is the first thing to try. Some discs (but not many) are now encoded in 7.1 and they will obviously be OK regardless of the DSP being used (or no DSP at all).
Second, if you play the test tones from your AVR, do you hear tones from all the speakers? I not, then they are miswired.
Can you post the trim settings from your Audyssey calibration please?
FInally, do you have Dynamic EQ engaged, which will raise the surround levels when you are listening below reference.