USB sends electric shock to sound card and speakers. "Boom" anytime it starts/stops/reboot
Since I installed Mountain Lion (july 2012) on my 2009 iMac, my usb ports send an electric shock to my external sound card anytime it starts/stops/reboot.
So my speakers make a sound like "boom" and I'm afraid they will be ruined..how do I control this shocks?
It NEVER happend with Snow Leopard and Lion. iOS always purchased on Mac App Store.
iMac (21.5-inch Late 2009), iOS 6.0.2