No matter how careful the installer is, creaks seem likely at some time.

When Spouse installed our - back in the early 1980s, he drilled holes
through the joists to atke the pipes which were going the 'wtong' way. He
also tried to save a bit of work by using a length of pipe which was short
enough to make it tight.

The creaking disturbed my sleep so much that I was distressed. He lifted
the boards, added a small piece of pipe and the creaking stopped.

... Don't fasten back the floor boards until you are sure you have got it
fixed as you are very likely to want to go back to it.

Good advice.

Most creaks seem to occur where there is a right angle bend and/or
restricted space.

True.

Many thanks for all the advice. The dripping sound is only noticeable when
the heating is on and I just assumed that if it was expansion it would stop
after a while but that doesn't seem to happen. I guess I can live with it
for now if I know the ceiling isn't about to fall in.

John