About a month ago I had some plumbing work done, about a week after that
I noticed a loud clunk when I turn the tap off (I presume an airlock
somewhere) now, in the last few days I have noticed that after shower or
toilet flush there is an annoying humming noise for several minutes I am
presuming until the main tank refills (in attic).

I wont be able to get a look at this for a couple of weeks due to other
work but what are likely causes?

thanks