Guitar amp with popping noise

Question

Hi, I own a "Torque T652GR" 65 watt guitar amplifier. (I can already hear you saying "oh dear") The problem I have with it, is that every now and then it makes a popping sound. Normally just the once and on the rare occasion after the "pop" the volume will drop and then come back up again. Any ideas what could be causing this anyone?Thanks Rob