amp cutting out

I have a  kenwood 4 ch amp running 4 51/4" speakers, i have had the amp for about 6 months now and just recently it has started cutting out when i turn the volume up to a decent level, i found that if i fade to the front speakers only the problem does not happen but if put any power to the rear speakers all the speakers cut out then come back on then cut out and keeps doing that  until i turn it back to front speakers only. if anyone has any ideas on what the problem is or what i could try to do to fix it i would appreciate it.

Assuming that your amp is in good working condition, an amp will display problems under 2 conditions. 1. low voltage in. check your power connections and ground (check it twice). 2. Low impedance between the amp output and the speaker (check out each rear speaker and the wiring) A pinched or shorted wire or burned voice coil will cause your amp to shut down.