Rigid Raider said:
DON'T go sawing and lifting floorboards all over the place until you have eliminated other possible faults as you will probably saw through a pipe and cause even more expense. Expanding pipes are a regular but diminishing crack crack crack, certainly not a loud banging, which only happens for a few minutes as the water temnperature increases and the pipes expand. If it is happening all the time it's some kind of airlock problem, which can be very hard to cure.
Clearly sawing through a pipe is not a good thing, but circular saws have depth adjustment. Lifting floor boards is a peice of pish for anyone with a modicum of DIY ability.
The expanding pipe in my bathroom floor made a godawful banging sound, as if it was being belted with a hammer. It kept everyone in the house awake as it was aplified by the floorspace and easily cured by fitting felt under the pipe.
Certainly good advice to go on a DIY forum but under the circumstances, without having someone actually inspect the system in person, the advice of one plumber (me) is as good as the next.
Dont know how much plumbers cost in your area (if you can even find one) but I reckon a couple of hours lifting floor boards might save BTFB several hundred quid.