My first initial reaction would be to check the cable....then the input jack on the amp, then on the guitar.
That is a god awful sound though. If the tubes are fine, and the fuses are fine...its hard to say what the problem is. Usually if you blow some resistors on the board, or blow something else on the board, it either will be very quiet with hardly any volume, or it wont make any noise at all. Sounds like maybe its something in the signal chain.
Tough to say what the problem is just based on the info you've provided.
Couple things I can advise is to clean the amp and make sure there's no dust inside, and to check the connections on the input/output jacks.
So it is definitely not the guitar or the cable or the input/output jacks on the amp. Checked it all.
The amp will work pretty will for about 5 minutes then it will start sounding like the above clip which leads me to believe it has something to do with the tubes? Hmmm...
This is my amp. I was playing it yesterday either the back off and just waiting for it to make the noise again. It did I unplugged the speaker outs and it still was doing it I could hear the tubes barely producing the sound. Also the power tubes were extremely hot. I swapped them with some other 6l6's that I have and it still did it. It seems like once the amp gets warmed up and played a little that a resistor to do with power might overheat. I know the devilles are said to be put together with fenders spare parts and whatever. So hopefully it's a resistor or something and not my transformer. I'm tired of dealing with it though so I'm taking it to a tech.
Sounds like the amp heats up, and as a result, a joint comes loose. I'd probably say it's a dry joint. Either:
- get the amp looked over
- have a look yourself IF and ONLY IF you know what you're doing and have worked with high voltagers. It may just be a simple "solder it properly" job. However, if you have never done electronics, and if you are apprehensive of large voltages (you should be, they can be lethal), then don't do this yourself.