I had new lifters installed 300 miles ago and it still taps from time to time. The dealer says run it for 1000 miles and then if you still hear it. Then come back and we'll check the oil pressure and see if you have a clogged screen in the oil pan or a gasket leaking air and foaming the oil. I was thinking about running engine flush an then putting in new oil-maybe synthetic. Is all of that safe for BMW-specifically the flush? I know the dealer would say no way.