Thought I'd toss this one out to the OMNI VI users: I have one of the early OMNI VIs, and it has always displayed filter "ringing" ONLY in the 500Hz filter position in CW mode. None of the other filters do this. Also, in 500Hz, when I use the PBT control, a continous "howling" occurs which changes slightly in pitch as the PBT is tuned. Any similar experiences or fixes? 73, Larry N6AZE