I wouldn't worry at all. It's the relative numbers (%) that matter, not the absolute ones. As the total number of your subs increase, the more you will lose in absolute terms, but as long as it's still more or less the same proportion of total subs, it's nothing to worry about. It's perfectly normal even.
How many did you gain? In analytics, for the last 30 days, what are the 3 numbers in those boxes in the subs tab? (subscribers, gained subs, lost subs) ? Don't post your figures here if you don't want to, but the calculation to do would be divide "lost subs" (3rd column) by "subscribers" (1st column) and multiply by 100 to give you your "sub turnover" Mine is 9.5%