Knocking Hot Water Pipes

Recently our hot water pipe started knocking when the hot water is turned off. This happens in both bathrooms located on the second floor of our house. What is causing this? What is the solution to stopping it? I found out that if I turn on cold water and then turn off the hot water, it doesn't knock. But try getting two teenage daughters to do the same. At any rate, I figured this was a plumbing problem. Our house is 16 years old--we bought it this summer.

Does this happen from any hot water faucet in the house, or only at one of them?

I have the same problem and the noise is very loud, like someone is using a drill or hammer noise.

this only happens when we turn on hot water in bathroom on the second floor ONLY.

thanks

From what I've read here, a loose washer or valve seat can cause this.

Knocking Pipes

Knocking pipes in the upstairs...pipes knock when the faucets are turned off AND when the sprinkler system is going...
Driving me nuts...particularly since my sprinkler comes on at 4:30 a.m. and the noise in the pipes awakens me