I am getting an oscillating or cavitateing noise from the plumbing when my toilet is filling. Not everytime. Its not anything in the toilet and water seems to be flowing freely into the tank. The noise is coming from the pipe in the wall.

Any ideas?

water hammer?

Water will not compress and pressure may be higher than the pipes were expecting - and no "water hammer arrester" (or vertical/void of air) was provided to keep the pipes from clanging (or whatever noise).

Say the normal water pressure is 50psi, and you are getting 75psi at your location as an example. without some pressure relief (i.e., the water hammer arrester) as water flows or is suddenly stopped or started the pressure of the water makes the pipes move and thus make a noise.

I will try the turn off the main and drain the lines fix tonight

Good idea. IF the water hammer thingy is the problem and you do have air pockets drained that should solve the problem.