I fitted a piper cam kit with antipump filters to my old S2, ran in as said and as have done many times, yet still noisy I took the anti pumps out and fitted new normal lifters and bingo... Quiet as a mouse

Could have been the anti pump lifters as never used them before.

Lots of things can make lifters noisy though

General wear and tear and age of lifters
Worn cam / lifters
Wrong oil grade or poor condtion oil
Low oil presssure

Hope this is of some use to you

Bri.