Nesting coal tits seem flustered

We have been so fortunate to have had the pleasure of a pair of Coal Tits nest in the eves next to our front door (fully visible from our front room window). We watched them take material in to the nest and then the behaviour changed to them taking insects and food in. However, recently we have noticed that the birds come back to the nest with beaks full, but seem to hang around on the outside, almost flustered, and then fly away. They seem to do this several times a day with the same food. We have been outside and there are no visible predators. We cannot hear any chirping from the nest (only scratching) is this bad news? It has been the most beautiful event to have watched in the last few weeks, and we are really quite proud. Can anyone shed any light please? Two very proud but worried Coal Tit adoptive parents!