I recently closed the supply lines to both my commodes for approximately two weeks to avert any water accident while I was away. Now every time they are flushed there is a loud machine gun like banging both at the area of the commodes and in the kitchen sink/dishwasher area. I open the fawcets in the correspnding lavatory and the noise is transferred to the kitchen area and continues until the sink fawcet is also opened and within a few seconds the banging stops until the next commode is flushed.

This had never happened before and the house is about 15 years old. Any suggestions?

All I can suggest is to remove the float ball and stem assemblies from the ballcocks and flush the supplies out. At the same time check to see that the washer's are seated correctly. Good luck, Tom