For the past few days, I have been experiencing vibration in pipes somewhere in my house. The vibrating occurs at random times when no water is being used, lasts for 5-10 seconds, and sounds like a small motor (think pressure washer) or hammer drill operating. I have tried to get to the basement to locate the sound, but it always stops before I can get there. The house has no sump pump, the heating is gas, and the water heater is 7 years old. My initial thoughts are a faulty flapper valve on one of the toilets, or a vibration in the pressure reducing valve on the water heater. Any thoughts as to what could be making this noise? Thanks in advance for the help!

Turn off the toilet water supply. Still hear noise? If no first replace the leaking flapper. The hammer or motor sound could be in the ballcock or PRV for the house. Go the the PRV and have someone tun the water. Then check ballcock.

My initial thoughts are a faulty flapper valve on one of the toilets, or a vibration in the pressure reducing valve on the water heater

Water heaters don't have pressure reducing valves... they have TEMPERATURE and pressure relief valves (also referred to as a T&P valve).

The reason I make the distinction so clear is because Ma0641 has mentioned the PRV... the pressure REGULATING valve (see image). Here, I am in agreement with all he said and want you to check all as he said... especially for chattering at the PRV valve at the water main IF it is present... ;)

Back to you...

Mark