[To Grind Or Not To Grind]

I no this topic been on here, but i need some help.

I was out riding today and when I was on the back wheel my brakes kept on slipping. I left it for a bit, thinking it was a bit of water on the rim/pad, but it kept on doing in. I'm using the new Heatsink pads witch are brill, before the slippin started! What should I do about it? Grind the rims? or just clean the rims and pads?

Thanks Matt :D :-

[Homemade Frames + Parts]

My booster! Works a treat!