When the toilet is flushed (upstairs), it sounds like there is a woodpecker in the pipes (wall). Very loud and startling. I have copper plumbing and a new tank system was installed this past summer in this toilet.

Sounds like the stop [valve under toilet] is fluttering. Is the stop opened completely? Possibly disassemble and check the bibb washer in it.

Knocking, popping, creaking and crackling pipes are a common complaint, especially in colder weather. I can tell you what's happening and take the mystery out of it but you're not going to like the repair. When a draw is made on a hot water line the line expands against a pipe strap next to a stud and when you drain hot water from your tub or shower it goes into a chase that is a little cooler then room temperature. The heat expands the pipe causing it to rub against the stud to which it is pipe strapped. This is the sound you hear. As it cools it contracts and the noise is heard again. To repair it you must tear open the walls and locate the pipe strap that's causing the problem and shim it tight. Most people when they learn what causes it just elect to live with it. Regards, Tom

Does this noise stop the moment the ballcock shuts off when the tank is filled? Can you hear the noise best right in the bathrrom where the toilet is flushed or elsewhere in the house?