I got this problem, it's cos of my front sprocket. Left foot facing up, it's loose, right foot facing up, it's tight. Try-all cranks, Onza sprocket (well old), CK hub I know it's not the right thing to do, but I set mine up on the tight spot, then spin it round to the loose spot and make it 1 click tighter. Seems to work alright, I never get chain slap, because the stays are so short.