I have a Tri-level and in some areas of my home I have low water pressure in others the pressure is just fine. I have a copper main in thru the crawl space. The service splits half way into the crawl space with the first line going outside to the front faucet. One going upstairs to the washer and two bathrooms. These all have low pressure. Another line splits to the bathroom downstairs this seems to be fine. The last line goes to the kitchen sink, dishwasher, and outside rear faucet, these are bad.

The funny thing about the whole situation is when I turn the water on, flush a toilet, take a shower then turn the water off, about a minute or more later inside the wall you can hear a trumpet or tuba sound. I think it is D flat.

My rationalization is there is some type of partial clog in the line somewhere between the splits. When you turn the water on the pressure at first normal and soon decreases. This leaves a percentage of the line empty. When I turn the water off it takes sometime for the line to back fill and when the back fill reaches the clog it presses the air in the line back thru the clog and it causes a trumpet or tuba sound.

I have attempted to remove all excess air by running the water starting upstairs and working my way down to the faucet outside which is the lowest elevation. This didn't work.

Anybody got a clue what it really is and how do I fix it.

Cut the main or remove the on/off valve and run a coil thru the line?