Garageband and usb distortion

[ariadri]

this is my weird situation. I have a sonica theatre usb sound card that works out of the of the box in snow leopard. I also have three usb ports( in wich my motherboard which is a p5ld2 by the way). I installed garageband with all updates and now I get a distorted sound like an echo on all outgoing sound. I figured out if I move the sound usb to another usb port. the distortion goes away.
now my question

is there any way to restore my distorted usb port (sort of like a reset)?
I deleted and replaced appleusbaudio.kext. iousbfamily.kext applehda.kext and also replaced my dsdt. file with no success.

any suggestion greatly appreciated