OK, I thought I remembered the high frequency crackle being in an
earlier version like 1.2, but can't specifically recall. If you have
the latest gamecode installed it should not be there. Did you call
Mike Pupo, he could help make sure the FF install went perfect.
Does the current FF setup have an adjustment for crossover of the
frequencies sent between the backbox and the cabinet speakers? If so
it might be an adjustment. On older versions I thought that was
controlled at the sub which might explain why you are hearing the same
problem when swapping the backbox speakers....
If there's no more crossover, I believe it would eliminate this
possibility. You may want to put the original cabinet speaker back
in place just to make sure.
The other thing I'd say was there were quite a few sound settings in
the game menu (I think it was meant to be video game like where you
could control sound of game effects versus voice effect....adjust the
overall mix). I played with them, but never noticed any actual
output difference. I'd confirm these are all set at factory as well
just to rule it out.