I know this forum has addressed this before, but I'm interested that the bluetits which have taken up residence in our box seem to be doing this hole pecking all the time, even though they appear to be feeding young. Also, i have not investigated the box, but although I see them taking food in, I cant hear any cheeping from baby birds. Should I be worried?
Maybe you are approaching the box too closely if you are able to say that you can't hear the youngsters cheeping ... there is nothing you can do except wait & watch from a safe distance to check if food is regularly being taken in, if it stops then you can assume the nest has failed and you'll have to wait until September before cleaning out ... regarding the pecking behaviour, two different answers here, the second one coming from RSPB
2013 photos & vids here
eff37 on Flickr
Maybe they are being ultra polite and knocking before going in . I would just watch and leave them to it. There is no need to be worried because to be honest there is nothing you can do - they have started and they will finish. Maybe you can't hear anything because the chicks are too small to make much noise to cover the distance.