Continuous hammering noise
When it is very quiet and you can hear yourself think go to your basement area and see whats hammering. You feel the pipe when the noise is happening and you will feel a definate vibration on the worst pipe in the worst area, thats where you put an expansion tank or a upward capped pipe, sometimes is enough to fix the hammer. Keep looking till you find offending area. Sure your stool isnt running every little bit? Or could be your hot water heat tubes, heating and cooling. If you put in an expansion tank, put a 1/4 turn steam valve just below it to isolate it so you can replace if nesessary.