My s reg renault scenic is havin a few problems?

i was driving home from work the other day when suddenly i heard a loud banging coming from what sounded like a valve banging the rocker cover , when i pulled over and had the bonnet up it was sounded fine at idle but when u put a little bit of power it made the bangin noise again. Ive had new coil pack, leads, and plugs and the valve clearances done and put new timing belt on as thought it could have jumpd a tooth. Any idei would be appreciated.