#1
Right, I've noticed that for the last couple of months now that whenever I turn on my amplifier (A Line 6 SpiderII 210) that when I plug the lead in it will make a buzzing sound, and I have to turn the volume knob on my main guitar (A Carvin DC727) up to full in order to eliminate this. However, as soon as the volume is shifted ever so slightly from full (on the guitar's volume knob) the buzzing returns and it is quite loud. This buzzing occurs when on both clean and distorted channels. When playing my other guitar (Jackson RX10D) the buzzing is prevalent at all times and overbears the sound coming through the pickups. I've tried using various leads but the buzzing still occurs, is the problem something I can fix at home or does it require professional help?
#2
could be a number of things.

have you played your guitar thru a different amp?
have you played a different guitar thru your amp?

any thing change in the environment, like you plugged a computer monitor or a microwave into same power outlet as amp? You'd be surprised how often this happens. Could be a loose guitar jack or other wiring or shielding problem with guitar.

?
#4
i think he's done that when he said 'tried various leads'.

i would take guitar and amp to a store and work on process of elimination. shouldn't cost you anything to do that and maybe someone will be helpful and help you try to narrow down. If it is the amp and it is NOT the input jack, then it may not be worth fixing.