I'm a new homeowner in a 1-1/2 yr old townhouse. My wife and I just discovered a plumbing issue. After she had flushed the toilet in our upstairs bathroom, a very loud "jackhammering" sound occurred (sounded like it was coming from behind the drywall). The only way it would stop is if I shut off the water valve underneath the toilet tank or if I lifted the floatball inside the tank to stop the water from filling the tank. No other toilets or faucets in the house makes this sound. Is this what is called water hammering? If not, what could it be? Is this something that a novice could repair or is this whre I need to call the pros? Thanks for any help/input.