Adjustable valves on both sides of radiator?

Wookey

Was the new pipework done with plastic or copper? Plastic pipes should be fairly quiet whereas copper will produce more sound due to thermal expansion/contraction when it comes into contact with timber, a dripping sound could be mistaken for this expansion depending on what the pipes are rubbing against.

Is the front of the box easily removed? If so take it of and check the visible pipe run for anywhere it is rubbing against anything and try and ease it or put something between the two things.

If no noise is occurring with the cover off then it could well be the cover that the pipes are rubbing against, try clipping the pipes back away from the cover in that case.

If the noises can be heard in the attic then one other possibility is the rad expanding with the heat going thru it, not as common but still can happen and would be more likely in an area with a far lower ambient temp, make sure the rad can move easily on its brackets as its the heating creating some minute expansion in the rad and it reacting to it thru the bracket.