Hi, thanks for the advice.
I've just played the factory presets through a 1/4 inch cable to one of my Alesis active speakers and I'm still getting the 'fizz' which is really pronounced on any setting that has some gain.
I have tested a variety of guitars, single coils, humbuckers and the clipping happend regardless. I've also played with the guitar impedance and guitar 'pad' settings but to no avail....
If it had tubes, I'd swap them out ha ha!
Any more suggestions would be appreciated, but am coming to the conclusion I'm going to have to return it. Groan.