Bottom Bracket noise

SunWuKong

Went out for a short ride last night and found that my bottom bracket seemed to be making a grinding noise. At first I thought it might be the chain rubbing on the front derailleur but this isn't the case. I did the Polka dot on Sunday and think this may well have something to do with it. I have and alu frame with no drainage hole under BB. The BB is the Shimano one for hollowtech II chainset.

Any ideas?