What's that noise?

One of the funny things about living on the boat are the noises you can hear. When you wake in the morning and the sun is shining through the skylight you can hear all the water birds outside. It's so much noisier than a usual dawn chorus, there is a lot of quacking, squawking, honking, cheeping, flapping and splashing. Sometimes there are fights and yesterday we woke to the loudest commotion, the amount of flapping and splashing, squawking and shrieking going on was deafening and then so much splashing as clearly a big chase was going on and it honestly sounded like they were trying to kill each other. We've seen swans fighting with ducks (the duck won!) Geese and swan fights, coots attacking other coots, they have this strange alarm type of clicking noise when they are trying to fend off attackers. Most of the fights seem to stem from protection of babies or food.
Then there are other noises you can hear outside, sometimes when we're moored in fast flowing rivers the fenders thud against the side of the boat. This can be really annoying and we try to remember to lift them out of the water before we go to bed.
Depending what we are moored against you can hear the sides of the boat rubbing against the side, when other boats pass we gently knock against the bank. Sometimes not so gently if boats are passing too fast or too close.
The other evening though I could hear this tapping sound and it was like someone was knocking on the outside of the boat. It got louder and was regular and I started to get worried that someone or something was trying to get in. The weird thing though is that Dex wasn't barking and he normally barks at anything nearby. The tapping continued and I asked John to go and check. He came back after a few moments and told me to look out the side window. Unbelievably it was a family of swans pecking at the weed on the bottom of the boat! Not had that one before!
I tried to get a photo, it's not brilliant but you can get the idea of what was happening.