MARK III Red Reverb Issue

Howdy yall. This is my first time on, as I have recently acquired a mk iii red stripe combo amp. Such a rad amp. Currently I am having issues when I turn my reverb up. When I turn it up, there is lou crackling and volume boosts, but when I turn it to 0 everything is fine. I figured it was a pre amp tube. Cant seem to find which is the preamp tube for the reverb though. My amp has two 6L6 power tube ports and 5 pre amp ones. I went through all of the pre amp tubes, with my one replacement pre amp tube, and couldnt find the port. I interchanged all of them but the port 1, silver encased one. Do I need to replace all of the pre amps and power tubs? Is it a circuitry issue?
Thanks so much for the help.

"When I turn it up, there is loud crackling and volume boosts, but when I turn it to 0 everything is fine".Do you get any reverb effect at all?

The reverb tube is V4.

v4 should be the one furthest from the input jack. The preamp valve set behind is the phase invertor.

I always had a hissing, buzzy noise problem with my MK3 whenever I used reverb. I cleaned all the connectors from the amp to the reverb unit. They could be rusty. What finally sorted it was a mail to Boogie. They directed me to make an additional connection to earth from a transformer wire and that eliminated all the noise problems completely..

"120k resistor on the red lead from the smaller reverb transformer to ground."

I am not sure if that was resolved by the red stripe - mine is the purple one before. It was called the 'reverb glitch mod' so seemed common to the amps. I have a copy of the Mark 3 mod sheet from Boogie themselves.

I also added a 10k 1/2 watt resistor in series to the black wire going to the fx return jack. That significantly boosts the amount of reverb available. 3.3k or 5k would work too

replaced the reverb pre amp tube. still happens. called boogie, and they recommended I take it to a tech.