When either of our two toilets is flushed,
we get a jackhammer oscillation in the supply
line until the tank is filled. Turning on an
additional faucet while the toilet tank
is filling increases the frequency of the
oscillation, so it seems to be related to
the volume of water flowing, but it occurs
only when a toilet is involved. It can't be
invoked by turning on two faucets, for
example. This plumbing has been in place
for 23 years, but this condition didn't
exist until a couple of years ago.
What's going on?

--
Charles Packer
http://cpacker.org/whatnews
mailboxATcpacker.org

When either of our two toilets is flushed,
we get a jackhammer oscillation in the supply
line until the tank is filled. Turning on an
additional faucet while the toilet tank
is filling increases the frequency of the
oscillation, so it seems to be related to
the volume of water flowing, but it occurs
only when a toilet is involved. It can't be
invoked by turning on two faucets, for
example. This plumbing has been in place
for 23 years, but this condition didn't
exist until a couple of years ago.
What's going on?

My first guess would be a failing washer somewhere in the toilet valve.
They tend to flap around when they get old. The valves are cheap enough
that it's not worth a repair--just put in a new valve assembly. While
you're in there, replace the flapper too.

My second guess is a problem with the shut-off valve at the wall. Try
closing and opening it. If that works, great, but it's unlikely. The
washer might be failing, or there might be some debris inside.
Sometimes just having it open a little more or a little less will help.

--
Steve Bell
New Life Home Improvement
Arlington, TX USA