Scratchy sound coming from microphone when I touch it

Hello, I'm trying to record with garageband and I'm getting some scratchy sounds coming from the microphone. I'm using a pretty high-quality microphone, which has never been dropped or had problems before. The mic is plugged into a mixer, which in turn is plugged into an external soundcard (audio interface), which I bought yesterday. The soundcard is plugged into my computer via USB (this setup became necessary as Apple removed the second audio port).

The audio interface is cheap (30 Euros). I've put off recording for about a year because everyone told me the device I needed goes for several hundred dollars. Then a friend of mine showed up with this cheap one and it worked perfectly. We recorded a whole song several times with not even the slightest of interference. So I was pretty thrilled, knowing I could just get one of these and begin recording. So I did that yesterday.

Now I've plugged it all in and this scratchy sound won't go away. When I touch the mic with my hand it gets much louder, so it's obviously some kind of electrical interference. My question is, how come it worked perfectly yesterday with my friend's device, yet now that I bought my own it's making all this noise?

Thanks to anyone who can help me out on this.