wrote in message
ups.com...
This knocking pipe problem is really strange. It is a weak knocking
sound 2 or 3 times per second normally happened at night time in about
half an hour after all water usage is stopped. Once it started, it
will keep knocking till the next morning. It really drives me crazy.
The only way I found that can stop it temporarily is using water like
flushing the toilet. It will stop the knocking about another half an
hour. So imaging that, wake up by the noise at 1:00AM, flush the
toilet, try to get back to sleep before 1:30AM, if not, flush again...
Anyone can give some advice?

Do you live in an apartment or condo or duplex? The problem might be in
another unit.