i doubt your main bearings are noisy... if they are i would be looking for another engine lol
your big end/rod bearings are mostly likely gone... how bad are they tapping... you will most likely need to get the crank ground, new bearings and also get your head and block cleaned as your bearing shavings will have gone right through it..
have you run your engine out of oil? or low? that is probably what caused it
good luck