Hows it goin

I'm not a car expert and I was wondering if anyone has had this before. I've just noticed a sound from my car the past couple of days. When driving along, at any speed, I would just be cruising along and then just take my foot of the accellerator and I can hear this low humming sound which sounds like its coming from the front of hte car. It kinda sounds as if the brakes on one side is grinding or something
I thought it might be gearbox, it still makes the sound when I put the clutch down though.
ANy help would be appreciated