The PLC must be started in at 33 rpm and switched to 45 on the fly. The motor doesn't have the torque to ramp up to 45 from a dead stop. The motor will just quiver.
This sounds like the problem I had with my PLC. It eventually got worse and actually made the sound worse. I would expect yours to get worse too. Hopefully you didn't spend a lot for yours.
The PLC was discontinued well over a decade ago when the SDS came out. The SDS is a huge improvement over the PLC. You should ditch the PLC and get an SDS.
I was considering but Mike from VPI said it wasnt worth much. I did purchase a Music Hall unit for about $300.00 thst made a nice improvement in my HW-19. Claimed that it works up to 2 watts snd the vpi is 3 watt draw. Mr Hall said it would work fine and it has worked flawlessly for a year now. Doesn't even get warm.
The PLC was the worst audio purchase I ever made and the only item that went to trash. Mine never worked properly, and after two factory replacements VPI ceased support.
+1 - on being a bad purchase.
As a goodwill gesture - VPI should consider putting an announcement on their website that anyone bringing in a PLC will be given a credit of $$$ ? toward another current VPI product. Like the SDS. It think it would be good for VPI business.
Mat W are you reading?