Air in lines

[brycesteiner]

With all your help I've made significant progress on getting my water leaks fixed. So far:
1. New Water heater (tankless) - works great
2. corrected some pex lines and crimped in new brass fittings and copper crimps
3. cleaned up and reinstalled shower drain (leaked)
4. water filler hose infeed to fresh tank (mice chewed?)
5. air escape line back to water filler connection (mice chewed?)
6. fixed outside shower
7. cleaned or replaced all of the aerators.
8. misc.

Now I've got something else and I've got my suspicions and just give me your confirmation or correct my thinking.
From the water pump to the trailer seem to be fine. It seems to hold pressure just fine.
From the water tank to the pump, however, is a different story. I noticed that once in a while I get a hum from the pump and see air bubbles like this:
https://youtu.be/U__Jdsc-a5A
Then when I turn the water on at any faucet, I get a bunch of air in the lines and the pump has to prime itself again.
At first I thought it was the winterizer valve, but after removing the hose, I don't think so as I think I would see dripping as the air comes in, water escapes.
I think I must have an air leak in the line between the tank and the pump. Replace that line, or do you have knowledge that maybe it's something else?

[Carl n Susan]

If mice chewed on the fill line and the vent line, why would they pass up the line to the water pump?

[brycesteiner]

that was my thought too, I just don't see anything other than the air in the line. I'll go ahead and change it and see if that works.

[brycesteiner]

That was it. I replaced the line today and no more bubbles. Now that that is fixed I put in the bleach in the water tank and into the lines - 1 cup for the 50 gallon tank.