Pipes making squeal high pitched noise? (washer, tank, drain, toilet)

[Teckeeee]

I am trying to figure out what is causing my pipes to make a high pitched noise only when the aftermarket water filter faucet is running or right when the water has stopped running, ie. washer filled up or toilet tank finished filling.

I thought it may be air in line since I drain the water heaters once a year but not even sure if that would make it happen? Maybe it's too much pressure in the system from the aftermarket water filter? I heard someone say it could be crud in the water pressure regulator bell?

It's been this way for a while before there was a water hammer and we complained to the water filter company and they redesigned it so less pressure would build up in their system. The only reason I am asking is we are planning to sell our house and don't need an inspection issue.