Rega RP1 / Bias 2 distortion issues

Hi, I've had my Rega RP1 with performance pack (Bias 2 cart etc.) for about a year (from new). The problem is that the first track or so of my records sound distorted, like it has fluff on the needle (its not that!). It first started in Oct or Nov when the temps first dropped significantly (maybe relevant?). I took the tt back to the shop but they couldnt replicate the problem, but the problem didnt go away when I set it up at home again. I video'd the issue to show the people in the shop. They thought it was a problem with the cartridge so kindly replaced it for a new one. Unfortunalely after only 2 trouble free albums, the problems returned. Not as bad and not every time but still very annoying!

I thought I'd pick your brains on here before taking tt back to the shop again.

Anyone had a similar problem?

Thanks.

EDIT: Just to be clear, the distortion comes in and out so the record sounds clear then disorted every second or so, just at beginning of the records (first track or half track).