I don't know if static is the correct word for the sounds that Pigin makes in Mint 7. It's more like your being electrocuted. It doesn't affect everyone apparently and in my case it's only pidgin that has the problem. But if you are similarly afflicted I may have a fix ( found it on Ubuntu Forums ):
Open Pidgin > Tools > Preferences > Sounds > Sound Method
Sound Command : play %s -r44100
It works for me, I hope it works for you.