decreased hot water pressure

Hello,
My husband & I are new home owners, we just moved into a newly built home in November 2003. Over the last couple of months we've noticed a significant decrease in our hot water pressure. The pipes (in all 3 baths) make that high pitched noise when the shower is running, the shower head in the master bath is not a pulsing head but now seems to "pulse" like there is a lot of air in the pipes. If someone is in the shower or the washer or dishwasher is on, the hot water flow is little more than a trickle if a faucet is turned on somewhere else in the house. We have a large garden tub separate from the shower in the master bath. When we first moved in, I could be running a tub full of water while my husband was in the shower--I can no longer do that. My daughter wasn't able to take a shower in her bath a few days ago at the same time I was filling up the garden tub in my bath. I have noticed that the stream of water has decreased by at least 50%, if not more, in the garden tub when no other water is running. A few evenings ago there was a great rumbling/vibration and I finally went down to the basement to see if the noise was coming from there, and it seemed to be coming from the hot water heater which seemed to be vibrating all of the ventilation ducts and everthing down there--my daughter was in the shower. We have only had that particular noise/vibration happen once so far. Our home is still under warranty with the builder and I have yet to reach him on the phone. In the meantime, any ideas? I've been reading about dip tubes, hard water and scale buildup. We have had hard water in the past and scale buildup and our water in our new home doesn't seem to be "hard". We have had no change in the cold water pressure. The master bath and bedroom is on the North end of the house, the kid's baths are on the South end, as is the water heater. We would appreciate any advice/guidance on this. Thanks.
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M. Montgomery wrote:

<SNIP>
The water heater is definitely a suspect. Although dip tube failures were solved some years ago, I suppose something might have happened to it. You mentioned rumbling/vibration from the heater. That can occur when the heater has been firing and the pressure in the tank is suddenly lowered (by running the shower, for example). If water flow *into* the heater were restricted, pressure would drop a lot and the rumble worse. Aside from the dip tube, it could be a blockage in the Cold supply to the heater, such as inside a shutoff valve.
Checking the flow rate from the drain valve on the heater would prove that the low flow was due to the heater or Cold supply.
Jim
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