Noise Mystery-Need Pro Plumbing Advice?

Is it a bathtub/shower if so see if the noise is there with just the bathtub running,if not the diverter in the tub spout needs to be changed.

The hum comes from the pipes moving/vibrating when water is flowing through.... Pipe clamps to stabilize the pipe will likely solve the problem.. If the sound persists after clamps have been added the vibration may be coming from a section of pipe going through a hole use spray pipe insulation/ rubber in these areas...

The hot water pipe is expanding and contracting with changes in the water temperature. This results in the pipe rubbing against framing members or other structures where the pipe is not properly secured or isolated. If the noise is caused from contact with framing, then extra strapping should be installed. If it is due to rubbing against something such as venting, the pipe needs to be isolated from direct contact by using something like rubber pads or insulation.

If you can put eyeballs on this pipe, it needs a couple of clamps to hold it tight to the rafters. That should take care of the problem.

Pipe is making the noise in this weather season changing condition. It is normal.