I used to get this weird "swooosh" sound whenever I used the Line 6 noise gate. I tried everything to get rid of it, new USB cables, new guitar cables, turning off all electrical appliances in the house, moving my PC to different rooms... Nothing got rid of it, so I just stopped using L6 sims altogether and just use my GuitarPort as an interface now.
Interestingly, now that I'm just using the GuitarPort as an interface, I'm not getting all those weird electronic swoosh sounds I used to. This has led me to believe that the problem I was having wasn't a hardware related one, but a software one related to POD Farm.