Occasional pop or snap sound from all speakers on ONKYO HT-R560?

ONKYO Receiver set to AUX input from Digital audio out on Toshiba laptop. Once or twice a month I will notice this loud snap or pop from all the speakers at once loud enought to make me jump out of my skin. The unit continues like normal after this pop sound but I fear it may harm the speakers. Has anyone had a simular problem and know what I should do?