Hi Riff Raff,

Being a metal gearbox and located very close to the electronics, you could be getting 'noise' interference from the gearbox which is unluckily for you, in tune with your PEC signal so that it interferes with your control............you did mention that the gearbox is stiff so you may find that by running the box in & applying lots of grease, the noise frequency will reduce enough to not give you a problem...............I hope this makes sense............Also, try changing the Xtal set to see if this makes any difference........if it does, then it would add more weight to what I am saying above...................

Cheers

CaptB