Hi. We have a whole house humidifyer attached to out forced air furnace. THe water supply for the humidifyer was a direct tap in to the hot water copper tube on top of the hot water heater. This year there is a lound low pitch humming sound that I believe originates at that connection. I have opened the valve as much as possible and it has not resolved the issue. For a brief moment I opened the sink faucet enough to let air in/out and not have water flowing and the humming stopped. Please help!

Confused.

How did you open the faucet and not have water coming out?

Doug asks a great question here. How did you do that? Does you sound happen 24/7 or just when the humidifer is drawing water? If it is the later then I think the tap valve has a loose washer.

Good questions. I ever so slightly opened the kitchen faucet before the water flows (it needs to be replaced)

The second question about when it occurs... it only occurs when the humidifier is drawing water and typically towards the end of the heat cycle when the system has been running.

I do know now the sound is coming from (at least a major part of) the extreme vibration of the pipe. My issue is that I am dialing the tap down to nearly closed to stop the vibration. This is causing the humidifier to not get enough water. Can that brass tap be clogged?

I think your tap has a losse and vibrating washer. Shut off the main and open a faucet somewhere to blow off pressure. Uncrew the cap under the tap's T handle and inspect the washer, replace or tighten. It is almost as easy to just put on a new saddle T.

Great. Thanks so much for the advice. Question though... the saddle T is mounted 10 inches above the hot water tank on the copper line that is the hot water leaving the tank to supply the rest of the house. Do I need to drain the tank when I turn off the main? Also, I'm guessing after I turn off the main I need to drain the system by opening a faucet at the highest point in my house? Thoughts?

You don't need to drain the system after shutting off your main but do open a faucet anywhere in the house. That will blow off pressure and allow to you to work dry and also protect your water heater from any possible expansion issues.