Would anyone care to diagnose my Vox Westminster?

[john.hostetter]

Hello everyone, I am new to the forum and to repairing amps.  My current project is my Vox V118 Westminster.  It worked wonderfully for two years but about 5 months ago it started doing this:  It powers on fine and sounds perfect for about 5 minutes, but then a horrible scratchy sound abruptly begins (the sound isn't static, it pops, hums, squeals...a virtuousic performance).  The guitar doesn't cut out, it can still be heard over the nastiness, but it's impossible to stand it for long.  I have heard that the caps in these things go bad, and that they are hard to replace.  I am going to open it up tonight and cross my fingers that it's just dirty.  If anyone has any ideas they would be greatly appreciated!