Humming in just the Hot Water line, when hot water is in use......

I just got a humming noise in the hot water line......It comes and goes while hot water is in use. Any answers to what's proboly a simple solution?

The first step, is to open up all the shutoffs to your faucets.
A partially closed shutoff can vibrate.

So I tried shutting the valve at the hot water tank , opened all the faucets and I must be on the right track because now the humming is constant rather than every 3 seconds....

Did you open the faucets?
Or reach under the counter and open those up?

I went to the shut off (main) and killed the water supply, went to every facucet and shower and opened everything including the outside ones too. Went back and turned on the water and shut each one off individually......should I have messed with the toilets? I have stems not the flaps. They look to be in good shape. It went away for a second then came back, but not as bad and its an intermitten hum now. Like once every 3 seconds for 2 seconds.

So, from reading your post, you did not go under the counter, and make sure the wall shutoff was open?
I don't care what you do with the faucets. That doesn't even matter.

The funny thing is, often I try to get people to follow this advice first, and they won't do it.
So then I drive out, take 10 minutes checking the shutoffs, and have to charge a service call for driving time.
They just don't believe that this simple check is needed.

But then that's why we get paid the big bucks.