Markbass Squeal on 9th fret E

Weird question - Markbass Rocker playing through P151 - getting a feedback like squeal on the E on the G string. Sounds like feedback or maybe a loud harmonic but I've moved several feet away from the amp and it doesn't change. Does it at low practice volumes and only when the note is played. All the other notes work fine Does it on two different basses. Is there something up with the amp?

 

Yes it does. Soldered into the preamp board so it would suck if the tube is bad. Everything sounds fine otherwise - distortion/grit is great and clean sound is ok (though the squeal happens on clean sound as well). The cab has a tweeter and i am starting to suspect that. Actually what I did was take the combo amp out of a CMD151p and replaced it with the rocker, which i like better. I can roll off a little with the VLE and it goes away. It just seems to be the one frequency that makes it squeal.

It's possible the combo heads are tuned for the tweeter but that would make no sense to me. Internally it's a LMIII including all the labeling internally. There are a couple of jumpers in there, some of which I know what they do but some are not labeled.

 

It's definitely the tweeter. I suppose I can replace it - looks like a LeSon Piezo dome tweeter. Or just disconnect it.