Lately after I flush the upstairs toilet only, there is a delay of about 10-20 seconds and then it sounds like a pipe or something makes this loud jack hammer until the toilet shuts off and the tank fills up. Why is this happening?

This loud noise is caused by a loose washer in angle valve or the fill valve, the next time the noise starts start to back off the angle stop located under the tank counterclockwise see if noise stops, next take the tank lid off and tell us which fill valve do you have, and will tell you the next step, Thanks.

John

We call this "seat chatter" and John's correct. This could come from the angle stop or the ballcock on the right. Good luck, Tom