More questions regarding my plumbing project of yesterday. I replaced
two valve stems in a shower/tub and had to clean out material that was
clogging what I assume are the valve seats due to low flow. I did
this by gently disturbing the material with a small screwdriver, then
blowing it out without the stems in place.

Today I tried draining the hot water heater since the hot faucet is
the one that was clogged yesterday. When I opened the drain to drain
the tank very little water came out so I turned the water to the
heater on to flush it out and let it run for several minutes. Then
turned the tank's water control off and still no water drained from
it. So I closed the drain pipe and turned the water back on to fill
the heater. Tank had never been drained before this attempt.

Then when in the bathroom where I replaced the valve stems a couple of
hours later, I could and still can hear what sounds like water running
behind the wall. Water flow in the tub was reduced for both hot and
cold this time, so I removed the stems and again there was this white
sediment clogging both valves. I cleaned that out again.

The water supply valve for the house is OFF, but I am still hearing
what sounds like water running behind the shower wall. No water
leaking from the valves or any faucet in the house. The water shut
off valve is just outside the affected shower wall. This bathroom is
the furthest site of water consumption from the water heater.

Could I have damaged something by running water through the hot water
heater for an extended time period? Or could what I'm hearing be air
in the pipes? Unfortunately, this does not sound like air. I'm not
getting how I could be hearing water running behind the wall with the
main supply valve off.

Any ideas?

Thanks.