I just ran a little test with your listed settings. I can’t really get that, unless I max out the Input & Output Gains. 184.108.40.206.
I added Mix = 10.0, maximum Feedback, Fdbk Path = All, toggled Speed to Full & Half, all Head Levels at 10.0 … Nothing like that, once you account for the feedback oscillation (and dial it back down).
Puzzling. Does it go away with the Filter at 10.0?