I have a Kustom quad 100 DFX guitar amplifier. When I turn it on there is a static sound with a faint popping sound every so often. It still will produce sound when plugged in to my guitar, but the sound persists.

I had not used it for at least two weeks, if not more, before getting this sound, and the last time I played it it worked totally fine.

What's the problem? what's the solution?