How does air get into the water pipe

Hello, the house has an oil central heating system and is already 60 years old. It started on Saturday. Strange noise when I turned on the kitchen faucet. There must be air in the water pipe. I turned it off and the water kept flowing for minutes. Then it started dripping and then it stopped.

In the meantime, it has improved. The noise is not as bad anymore. Less water runs when I turn it off.

My neighbor has built a pool on his roof. I hear a noise there. It is supposedly the cleaner.

Now my question is, how can air get into a water pipe? From the neighbor, from dryness, it hasn’t rained here for weeks. What should I do? Just wait until it goes away by itself? Thanks and best regards

I turned it off and the water kept running for minutes.

Magical faucet? When I turn off my faucet, no water comes out at all. P.S. Hot water or cold water. These are different pipes.

Now my question is, how can air get into a water pipe?

Through a defect - broken pipe, defective fitting, etc. ==> Call a plumber