Tapping/clicking noise in the corner of the upstairs floor

That sounds like either water hammer effect or expansion issues. Water hammer effect is caused by too much water pressure so when the water starts or stops flowing there is a wave of pressure from the flow of water changing too quickly. You can either reduce the water pressure, either by closing the water stop cock a bit or putting a cup on the main water tank ball cock if it has one, or fitting a device to reduce the water hammer effect, but that needs a plumber, or finally you can find where the sound it made and pad that point or fit it more securely. If it is expansion, then there is a small amount of movement somewhere in that area and again, pad the point where the noise comes from. This might have to be done by getting a bigger clip that holds the pipes and putting a thin bit of foam or rubber round the pipe and then put the clip on. The only other thing it is likely to be is cavitation which is caused by having air in the pipes. Try bleeding the radiators, etc. If all else fails, you will need a plumber to investigate.