I have a water well and when the water is running it is like I can hear the pressure in the pipes fluctuating (going up & down). Water flow at all faucets, washing machine, etc. fluctuates. The pressure switch was replaced but no change.

It is possible that your pressure tank is water logged, meaning that it has very little air in it. The tank should be about half water (bottom) and half air (top). Most tanks use a membrane called a bladder to separate the two. If the bladder ruptures, then it's just a matter of time before the air dissolves into the water, thus the tank becomes waterlogged. Check that by depressing the little tire valve at the top of the tank for a few seconds. If water comes out, then you have your answer.