I'd adjusted the handbrake too tight at the wheels when I fitted the kit and was getting some lovely harmonic groaning, particularly when reversing. It's hard to look cool when your car sounds like that hehe
So on the weekend I finally got around to adjusting it as per the instructions (duh!) which is all the way off then tighten it a quarter of a turn. This has completely sorted it so happy days.
The adjustment seemed to hold up well over the last two months but I'd like to see it last almost a year before I'd call the kit a cure. Fingers crossed...