My 04 Pista BB has the intermittent clicking going on; I've heard that these are garbage if moisture, grit, and grime are even within 20 nautical miles of it. My first course of action will be to ensure tightness, but another deal is replacement. From what I've learned, the BB and Truvativ crank go hand in hand. What aftermarket combo are you guys running once the ISIS craps out? Thought the noise might have been my speedplays, but replaced with flats with the same noise. I did have to use a cheater bar to remove the crank arm bolt, could that cause overtightening of the BB?
my drivetrain was clicking too and making all kinds of different noises after riding one day till my crank fell off. it turned out my crank was worn down from riding with it loose and needed to be replaced. luckily i didnt have to replace the BB. you can get ISIS cranks by themselves (it took me 5 LBS's before i found one) but I definitely wouldnt recomend ISIS after this experience.
I've had Truvativ BB's on a few MTBs in the past -- including their most 'bombproof' downhill model -- and they all developed annoying noises after not too long. I definitely don't reccomend them either.
cartridge BB's can be prone to clicking once they get a little worn. it doesn't necessarily mean its toast, but if the sound doesnt bother you give it a thorough check to make sure the bolts aren't loose or that the BB itself has play or runs rough. most any cartridge BB can develop clicking. not just ISIS.