I turned on my amp today (My trusty Blackstar HT40) and turned the master volume to the modest 11 o' clock position but I started listening closely and there's a weird "uuuuuuuuu" sound coming from the amp even when I'm not playing. My cable doesn't seem to be the problem but I tried another one to be sure but the problem is still there. The amp is less than one year old! I've carried it around to places and sometimes it'll bump into the walls and such but it isn't a ridiculous pounding. I really hope that isn't case.. Does anyone know what the problem could be?

I appreciate the help guys.
I am no expert at this (I just saw this question since I am in the sub-forum ), but maybe I could still help you figure it out.

Was it second hand?

did you drop any liquids or anything on it recently?

when did you last try it? possible interference from something?
This will start a RIOT! in me
Well I use a Boss Driver and Ibanez Tubescreamer along with a Boss CE-5 chorus but I didn't have them on today. Just the footswitch and the amp itself. It wasn't second it because I bought it new from a local guitar shop. I haven't dropped any liquids or anything but the last time I tried it I had to crank it to around the 7 position to match up with another guitarist and I was feeding back pretty bad but I eventually turned the gain down and it fixed the problem.

It's been really cold recently too but everywhere I set the amp it's warm, could it get damaged from carrying it to the car during cold weather? Thanks for the help guys, I'm trying all different kinds of settings to see if it's simply too much volume or something else.
A high gain amp is going to have some inherent white noise because of the amount of gain the amp is pumping out. How loud are we talking, when compared to the guitar signal?
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Try it on different outlets, and even in different rooms. Sometimes your amp can pick up interference from the wiring in your house, or other nearby power supplies, fluorescent lights, etc.

How much gain are you using? Too much will cause humming every time, on pretty much any amp.

Try plugging another guitar into it as well. Could be a grounding problem with the guitar.
Quote by tubetime86
He's obviously pretty young, and I'd guess he's being raised by wolves, or at least humans with the intellectual capacity and compassion of wolves.

You finally made it home, draped in the flag that you fell for.
And so it goes
'uuuuuuuuuu' to me says ground loop.

If it was just high gain hiss, he'd not be describing low-end hum.

Take the amp into another room and plug it in to a different socket. If the problem persists, return here.
did you hear a "ffffffffffffffff" before the "uuuuuuuuuuu"?

I wondered why the frisbee was getting bigger, then it hit me.
Quote by gregs1020
did you hear a "ffffffffffffffff" before the "uuuuuuuuuuu"?

Took me awhile to get that lol
Took the amp to band practice and the "uuuu" sound was still present.. I moved it around to different sockets. The thing is that I hear a tiny rattling when I hit notes on the low E around the 10th fret and higher. It's just rarely there, I'm not sure if that's the tubes or the speakers..
It sounds similar to when my amp had a microphonic preamp tube. Tap on each one with something non-conductive (typical suggestion is a pencil) and if you hear the tap through the speaker at an unusually loud volume relative to the others, replace it.