Further to my post on "strange sound on movies", I found the following information regarding movie audio:
If the average level is low, an AGC (automatic gain control) circuit will raise it; if the average level is too high, the circuit will bring it down.
While someone is speaking, the level is constant. When there is a break in the dialogue, the background noise can be heard to increase until it is as loud as the speakers's voice. This momentarily makes unwanted background sounds, abnormally loud. When someone starts speaking again, it is then instantly reduced to where it was before. This is annoying to the listener.
If there are subsequent audio processing circuits, the problem can get progressively worse, as each piece of equipment further increases background noise.
To my great disappointment, 3 days ago the Turner Classic Movie Channel, began gain pumping.
At one time HBO, one of the few commercial-free channels had gain pumping, but thankfully they stopped it.
I hope that Shaw will do something to eliminate this irritating audio problem.