Snap, Crackle and Pop
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[For non-Australians, the above is the slogan a local cereal company uses to advertise a tasteless soggy mess called Rice Bubbles].         

Symptom : Your monitor produces snapping or popping noises, and sometimes goes unaccountably blank after being switched on for a while.         I have no idea why this problem seems to affect Commodore monitors so badly. It is caused by arcing of the EHT rail (around 14kV, from memory) to lower-voltage areas of the set. Initial treatment is to turn off the monitor, leave it for a couple of days (to allow capacitors to discharge), and then to remove every last speck of dust from the inside. This usually works.         

If it does not, however, sterner measures are called for. Open your monitor and (here comes the dangerous part) leave it running, open, for a few hours. If you actively work against Murphy's Law by watching it from behind something or inside something, where the monitor can't see you, you MAY eventually be lucky enough to actually catch it in the act of arcing. Mark the place with a spirit pen and spray on some anti-gaussing compound. (This stuff has a very high dielectric constant and hence helps to prevent arcs).