I just finished putting together a used tub, it's an early 90's Cal Spas Eliminator series spa. We put in a new motor and wet end, and did a lot of cleanup, and I think I've got everything working now. The interlock switches for the cabinet doors has been "bypassed" by shorting the cord since the doors were badly damaged and falling off. If I get everything turned on with the interlock plug disconnected, then connect that last plug, there is a loud buzzing sound coming from the control box. If I unplug it and reseat it, I can get it to go away about 1/3 of the time. Sometimes it will slowly come back over time though, and it's a rather loud buzz. I pulled the panel off the box and it appears it's the large relay in the upper right corner that's buzzing. It's almost as if the solenoid is pulling the relay too hard or something. Is this something that may be fixed easily, or do I need to replace the whole relay?

This is generally caused by rust or dirt on the relay laminations - it won't harm it but is annoying - try a can of compressed air and blow it as clean as possible - if this fails, replacing the relay will get rid of your noise