Its got to stop sometime after its been unplugged. I do not think there are
any relays in todays plasma power boards, so the ticking is likely coming
from a transformer. Its a ' special effect ' that happens when the power
supply is loaded down somewhere, usually on one of the main DC outputs. The
overload condition triggers an imbalance in the feedback circuirty, and the
power supply cannot sustain itself with this condition present. You may want
to check the temperature of the big heat sinks on the X-sus board at the
peak of the problem, could be they are very hot.

About the ticking.. It doesn't stop even with the power removed. It is
almost if something is expanding and contracting, but makes the sound
equilivant of a relay?!

The really strange part is it doesn't seem to come from one consistant
place..