6V6 Plexi buzz

[Cathode_ray]

Built a 6V6 Plexi (actually an "October" build) and have been very pleased with it. Added the "Hot Switch" mod and this is cool as well - but the gain is a bit much for my taste. I'll work on controlling this later.
My issue is the overdrive is a bit buzzy at low levels. Anyone else encounter this,  and perhaps recommend a solution?

[PRR]

Looks like a filter-cap can (buzzy DC) directly behind the V pots?

[Cathode_ray]

Not hum/buzz but the break-up has a buzzy quality. For example with master vol. low and pre vol turned up.  This seems common to preamp distortion schemes but I've heard amps without the "issue".
At high levels all is great!