I’ve had my M-Audio interface for a long while now. When I record audio on this thing, I always hear this strange humming sound and I always kept thinking it was either coming from the guitar or microphone but turns out it’s neither. I just found out that the electric humming sound has something to do with a ground loop issue… from the website:
Hum/Ground Loop/Electrical Noise

If you experience a constant humming or low frequency buzzing you probably have a ground loop.  Try connecting all devices to the same power outlet on the wall.  If you have a laptop, disconnect its power supply to see if the hum/buzz disappears.  Please see this guide for assistance with troubleshooting ground loops.

If I figure out the ground loop which should be easy, I should be able to get rid of that annoying humming sound and I’ll be able to record perfectly clean then. Can’t believe I just figured this out after all this time!

I may not have to buy a better Audio interface at all!

Kev