Vibrating, noisy pipes

Hi! I need advice. My pipes will intermittantly buzz and vibrate when the water is turned on. We called the water company, who replaced the meter. It stopped for a week, and has just started again, only now the pitch is different. It mainly happens when there is a low flow of water, like after flushing a toilet. Could it be the water pressure regulator? Or something else? Is this something serious or just annoying? The house is 50 years old. Pat

Same thing happens in my house. It happened to me after I installed a water regulator. Sounds sortof like a car horn .
The pressure from my meter to the house was anywhere from 80-110psi. It was way high so I had to install one. I think whats happening is the pressure from the street is so high that the diaphragm inside the regulator starts to vibrate madly as it slowly is closed off from the spring pressing down on it, as your toilet water supply valve is closing. Ive seen the same thing happen on larger scale with the regulators we have at my plant. As for fixing the problem I'm going try to raise the pressure output of my regulator and see if that helps any.
If not I might have to put two regulators in series and try stepping the pressure down.