Leisure Bay Spa - Loud buzzing from circuit

[DrH]

I have a Leisure Bay spa with a 2-speed pump in a 240V configuration. The circuit board is a Balboa 52100.

The spa had been sitting empty and idle for a few months, and when I filled it up and switched on the breaker, a buzzing sound came from within the controller box (see attached photo). I let it go for a few seconds before switching it off. The pump never started, but the blower motor would when activated at the control panel.

I removed the controller box cover and immediately noticed the AC input terminal block was melted, the worst at the black wire terminal (1). I replaced the terminal block and switched power on again, just to hear the same buzzing sound. Then I disconnected the heater leads from the relay (2) and transformer (3)--same result.

After some searching online, I started wondering if the pump wasn't able to turn freely. That's when I noticed the slinger was split, I replaced it and the seals in the wet end. I found no issue with the motor turning.

I am still getting the buzzing sound as soon as I flip the breaker on. In the midst of the buzzing, I can hear a single click of a relay and I hear it click again when I flip the breaker off.

Interestingly enough, when I unplug the pump from the controller box (4), there's no buzzing. I do hear the relay click as before. I probed the the red and black leads in the wiring harness and read zero voltage when the breaker was switched on.

It is difficult to pinpoint exactly what component is buzzing since I won't leave it powered for more than a couple of seconds at a time and am hesitant to get too close to it. It seems the sound is coming from the vicinity of the heater relay (2), but I'm not 100% positive. I would appreciate any suggestions.