Noticed a slight tapping coming from the engine. Engine is relataivley a new rebuild. I changed the cam and lifters and it seemed so much better, however....

Cruising back on m4 last night and i casually went to overtake a lorry. Didnt drop down a gear, just slightly boosted to about 3psi. Hardly any acceleration at all and I could hear tap tap tap tap very very loudly. Any ideas????

Please dont say rebuild unless u have too