The interference with the mouse is strange but I have experienced it myself although only with older machines. How old is the mainboard? How old is the soundcard? Is it indeed a separate card? Do you have an onboard sound controller too? Is it disabled in the BIOS, if not do it. How loud is the noise if you use speakers or normal headphones? Latest firmware/drivers? Are you using a surge protector on everything, if not try with/without.

These are just things I would check and question if I were in your shoes. Of course you can also get another card but depending on what the warranty is like that may not be practical/possible.