Bob's Bird Box

 Hi Bob, welcome aboard. It sounds to me like very normal nesting behaviour and many of us are seeing it at the moment  personally I think if they have chosen your box then they were very happy with it so I'd just leave things as they are. They do tap on the windows just to ensure they are sturdy I think. Looking forward to keeping up with your nest. 
I have bluetits nesting in one of my boxes and today I watched as one particularly long piece of grass went in and out at least four times until she was happy with the arrangement.