Help needed- Warwick preamp "pop"?

I'm not sure if this is the right forum. Moderators feel free to move or delete if not.

I have an 1989 Warwick Thumb NT5 that has started popping very loudly when I use the push/pull to go from active to passive. Its the cringeworthy sound your bass makes when you forget your amp is on and you plug in or unplug (yikes). I've never had another of my active basses make this sound, so I'm not sure what to think...

Everything works fine when staying in either active or passive mode- it's just switching between the two that is painful- so I assume it's the knob and not the pre-amp, but I hope the experts here can weigh in.

I'd like to get this fixed, but not sure if it's just the Push/Pull knob that I need to replace, or if it's the whole preamp. Does anyone here have any experience with this issue that can tell me what I actually need to replace?

If it helps, mine looks like the pre-amp pictured here, which I pulled from an older TB classified listing I ran across while researching this issue.