speaker problem

quick question
after months of problem free listening, when i turned on my amps and cdp tonight i heard a low crackling noise coming from my left channel, specifically the tweeter.
powered off and checked all connections, ics and speaker cables, and everything seems in order, nothing loose.
when the power amp is off, no noise whatsoever.
is this a sign there is something gone wrong with the left tweeter?

associated equipment:
rogue mag 99 pre
rogue 88 power amp
metronome cd1 mk1
msb link iii
alpha core ics
alpha core mi2 sp cable
ps audio 600

any thoughts? i listen everyday for hours and have been for months w/o this problem.
thanks in advance

fujindemon