PC Speakers set up

[Scarlett]

My very cheap speakers started to make a raspberry noise whenever they were switched on. I had a look and saw that one of the USB connections was squashed. I have just plugged in some different speakers (mains lead and one jack for the sound card) and immediately it starts making the farty sound again!

Any ideas? Also I have an externam sound card (audigy 2 ZX) which I have never understood. Am I supposed to plug in the speakers into the back of the PC or the external sound card? When in the PC I get farting and I can't find an input on the ex sound card that fits.
Help please!!