Ground loops

[mickomoo]

This actually has nothing to do with music making, but since you all use audio gear and I'm at my wits in I figured I'd give posting here a shot.

I'm using a mic into a laptop to record voice audio (podcasts, lets plays, other commentary). I started last September with a clip-on mic (Zaleman Zim,cheap but adequate omnidirectional mic). There was always a hum, and I used audacity and Adobe audition post recording to edit it out as best as I could.

My original assumption was that the mic was picking up fan noise so I got a USB mic for Christmas (a Cad u1 USB mic). The Cad being a slight better mic picked up this background noise even better than the last mic. With a bit of research I narrow down the suspect to a ground loop and over the last two weeks have thrown everything I could at the problem.

I bought a surge protector that has a rfi/emi filter. Nothing changed. I bought plug in filters (from 2 brands) that are plug adapters which supposedly are supposed to filter out the noise signal. I also bought isolators... basically nothings working. I was going to rule out ground loop as the issue but last night while testing my usb mic I realized that when I place my hands on top of my laptop the buzzing goes away almost completely. That has to be a ground loop right? And my assumption is that the wiring in my apartment is poorly/not grounded. It's not my power adapter because it's 3 pronged and my outlets are 3 pronged as well.

Have any of you dealt with ground loops in your recordings. Especially with mics? I know it's highly unlikely that any of you record audio with usb mics, but I'm sure some of you have used laptops which are prone to having this issue.