Intermittent Problem

My friend has a Z22 with a sony Xplod radio......whenever he turns on his radio, his front right speaker makes a little POP sound .... also, OCCASIONALLY, his radio won't produce sound, it will light up, display everything.....but no sound and when it does that....after several times turning it on and off.....it will play sound again...........we checked the wiring, it's all good.
Could it be the radio ?
thnx for any input