Question about EMI and how to get rid of it

[detex1]

The spectrum may help:

View attachment 500260
looks like there's something very wrong, all over.
Are there any motors around there running at 1000-2000 rpm? Like fan or something?

Also, some ground issues for sure.

Fans nearby? Not that I know of

I guess the blower fan for heating is usually on, I'll try to see if theres any correlation

 

[detex1]

Take it to a friends place in a different neighborhood.
What kind of signal input: RCA, XLR or digital?

It's XLR input

 

[xanalog]

I did see posts about the Fender FRFR cabs but they seem to mention humming, buzzing, or hissing, which apparently were present on early production models. Mine is a later model for sure.

As shallow as I got in to that gearforum post; there were a few replies about the internal 'preAmp' board possibly being the culprit. Since its design is said to be decades old (in comparison to the powerAmp PCB)...