Mate - I have been having the exact same problem.
Drove me mad and nearly blew my speakers (and whats left of my eardrums)

But like you, I isolated the problem down the othe waves eq's. If you save the eq setting and then reopen it it fixes it.
No idea why. I find SX2 buggy and it crashes and sticks a lot.

But I am a bad person with dubious copies of cubase and wavez, so I can't really complain...