The ultra linear amps I have worked on did not include a choke...and from what I understand, running the OT in UL mode does not require such. THey have been very quiet. I would check the grounding location for the main Filter Caps and the HT from the PT. I have always found the careful selection of where to ground stuff, and with WHAT...makes for a quiet amp.
you're probably right but i racked my brain with this amp and the choke solved it and it sounds great, so i'm not touching it anymore.. thanks though