Polo Bikes

bbs normally grind rather than crack in my experience

Yeah, exactly, that's why the cracking noise is worrying me...

I'll have a good look at the frame later.

I'm not having much luck with bikes this week, my fixed cog slipped on my langster the other day, I haven't looked at it yet, but I fear it's probably threaded the hub.

is it a shimano number? if so it should surely last longer than 6-8months of summer riding?

Can't remember, need to check. Remember that it's rotating twice as much as on a normal bike, and i've been playing 4+ days a week since I got it, so it's had a lot of use.