water pipe makes noise

Hope some one can shed some light to my prblem. Recently my water pipe started make some grunting noise. It sounds like that you put some heavy stuff on a wood shelf which is going to crash. I thought I had problem on my floor but find out it is my pipe later. The noise comes from very begining of the pipe. It is right after the hot pipe comes out from the water heater. Since both cold water pipe and hot water run next to each other I can hardly tell which is making the noise. The noise will gone when I open a faucet or use my toliet but it comes back after that. I was told that it could be the air for somehow goes into the pipe. I was suggested to open all the faucetes and toliet but turn off the main faucet to drain out all the water and then turn the main faucet back out to let the water run through all the pipe for a while. I did but it did not solve my problem. Any other idea?
I recently use a 1600PSI pressured washer. Is it the problem?
Thanks in advance
Samuel
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Sam Hou wrote:

Turn off the water supply to just the toilet. If the grunting stops, the toilet fill valve (ballcock) is faulty. This is a common problem with certain models of ballcock; has nothing to do with air in pipes.
Jim,
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