I am building a new home and the plumber just finished installing a recirc pump system. I now find that when the recirc pump is plugged in there is a constant buzzing noise coming from a soaking tub in the master bathroom. I can't tell exactly where the noise is located but it is somewhere near the faucet on the tub or underneath the tub. It's not a jetted tub but a soaking tub only. When I first heard the sound I thought someone was operating a chain saw in the neighborhood. It sounds like a distant chainsaw or kind of like a bumble bee buzzing. It is loud enough that it is easily heard and annoying. When I unplug the recird pump the noise immediately stops. When the plumber turned on the kitchen faucet (about 50 feet away) the noise in the bathroom stopped for a couple of minutes but then came back just like before. The plumber thinks it might be caused by air in the line so he installed an expansion tank on the water heater but that has not helped. He seems to be stumped as to the cause of the noise also. I would appreciate any help you could give as to possible causes of this noise. Thank you.

There are really only two causes of noise of this type.
1. Vibration passed along the pipe via the pump
2. Valve gaskets flapping

You should be able to stop the noise, by grabbing the affected pipe. Secure that pipe. Done.

Sounds like a defective pump to me. More specifically, it sounds like the pump has defective bearings.

Both good answers. Take your hand and place it on the pump and if you feel vibration then replace the pump under warranty. Your pipes can pick up noise and carry it throughout the system . This is called " sympathetic vibration" and is common with vibrating ballcocks. Regards, Tom