In all the posts I have read on this subject... and the answer I didn't get from a Nortel engineer, I'ld say there is no real easy fix. There was probably noise before the new sets but new sets often wake the customer up to being a bit critical after spending money. I have found the noise to differ from KSU to KSU, be it a Mod 8X24 DR1 to an MICS Rls 4.1 there appears to be no pattern. If you do figure this out please TELL ALL OF US.
Rgds
PhM