Pipes making loud Shrieking noise

Whenever someone flushes a toilet (any of the three toilets) the pipes make a very loud piercing/shrieking/whistling noise for about 10 seconds. Whenever someone runs (usually) hot water for the first time that day from any of the four faucets, the pipes also make that horrible noise. This just started happening a few weeks ago after my dad was messing around with the water heater. I don't know what he was doing but he kept turning the water (or main water) on and off several times a day. He might have been cleaning something or doing something with the water conditioner, I don't know. But shortly after this the pipes started making the shrieking noise.
Anyone have any ideas on what the problem could be?
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Prime suspect (for me anyway) would be the washer is loose where he was shutting off the water. We had a washer in a hose bib that was loose and the sound was deafening.
On 9 Sep 2004 23:07:58 -0700, snipped-for-privacy@yahoo.com (Mike) wrote:

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snipped-for-privacy@yahoo.com (Mike) wrote in message

Poltergeists. Get out, now!!!
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Mike wrote:

You'll have to play detective. Could be one of the toilet fill valves (ballcock). Try shutting them off.
Could be a pressure reducing valve (would be located near main valve). These can shriek when at end of life. Or a shutoff valve not fully open. Dad may have thought it was opened when it wasn't. Or a shutoff that has failed internally.
The other suspicious thing is that water use first thing in the day sets it off. That makes me think of high system pressure either due to thermal expansion or a failed pressure reducing valve.
If you don't want to call someone in, your next step may be to buy a pressure gauge. You can get one that screws onto a hose connection, such as the water heater drain valve. That will tell you what is happening.
Probably dad didn't do anything "wrong", but rather turning things disturbed some part which was about to fail.
Jim
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Speedy Jim wrote:

I think Jim did a good job and covered almost everything. I have one to add, but after reading it, return to Jim's reply because you should not try and go back to the way it was. If I am right, then you want to add a pressure reducing valve.
If you don't have a pressure reducing valve or if it has failed, someone may have partly closed the main valve. You may never know, but it so it is an indication that you need to add or replace the pressure valve.
--
Joseph E. Meehan

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