windshield washers and the radio???

[bksmith]

I have a 2002 S60, 34K miles, no prior electrical problems - until the past 2-3 months. Whenever I need to apply the windshield washer (never a problem with wipers only), the back (left side only, I think) speaker makes a shorting-out, zappy noise. My local repair guys can't seem to get their act together and figure out the problem - any suggestions out there? All hints greatly appreciated!