May or maynot help with your situation...
I remember sweeping SA taps with Phillips amps & les using SA Nodes... When sweeping the amp or le I would come up with problems that looked like suck-outs, but after removing the locking terminators on the output tap (right off the amp or le) my suck-out would vanish... I took pictures of this phenomena... with one terminator, with two terminators, with three, with four and with out the tap housing and then with the tap housing in, yet not tighten down...
If this helps... .I can send you the sweep graphs for all these... just email me...
-Chad