Wired noise coming from amp

I recently played in a large auditorium for a school concert, and I noticed this weird noise coming from my amp. I first noticed it when I got my traynor amp, so it is not my cabinet. I tried it on a peavey 215 and still got same noise. tried changing basses, still got it.

whenever I play a 5th fret E string to 8th fret E string, I get a terrible, muddy, low almost farty sound. I tried rolling off most of the bass, but still got this terrible sound. Its way louder then any other note, and it just sounds terrible. It rattles the hell outta everything around it. If i barely touch the frets in that region, I still get that sound. when I play it in my room, I still get that sound. So I think its not a resonant frequency.

Could this be a tube issue? what is wrong here?

 

took it to a shop today, tech guy looked at the tubes and none were blown, the tubes are practically brand new. I'm reluctantly going to have to dish out 100bones to retube this, even though these are new tubes.

oh joy.