Ignoramus19021 wrote:
I have not used my phase converter in a while. When I fired it up the
other day, the main Allen Bradley size 2 starter made a very loud
noise, like a old style 60 Hz door buzzer. Despite that, the converter
ran, but I decided to not use it and investigate.

This is a Size 2 starter starting a 10 HP motor.

So.

What would be the proper troubleshooting procedure here and what is
likely wrong? Any ideas?

step 1, run to usenet. Skip the part where you examine what's causing the
sound in the first place, and then try to remedy it.