hum

Hi there A bit of an electronics novice here, forgive the lack of knowledge. But I'm trying to record my voice to my laptop via a USB-powered audio interface (it has USB cable for both power and data). A low hum has appeared which gets worse if I touch my mic body, and almost goes away...

I'm trying to detect the source of the problem and hope you can help me to where should i look for it. So when I'm raising the volume on the amplifier the hum gets more quiet then if its 0 volume.(Without any input, just the speaker connected) It's not ground loop probably. Already checked.