It begs the question, could anything be introduced into the motors to dispel water/moisture? Such as WD40 or lotoxine....
try loosening or tightening the screws that hold the vacs in place .I had that sort of problem when the vacs weren't tightened properly .Hope it sorts it for you .Other than that wouldn't know
Brendan iam having bother to mate with my vacs on my Powerflight mines only 3 months old did you get your vacs replaced under warranty or did you have to buy them. Darren