is it a fender frontman? cause i have one for a practice amp and it does what you say. It also could be incombination withthe pick ups. Some hum because their a little cheap, while you could also need a tune up with your guitar. I find if you place your hand on the bridge or anyhting metal touching the strings you get rid off the sound, but you can play with or get rid of it as the others say....what is your guitar?