Not looking forward to your shower giving an operatic performance every time you bathe? It's a pretty common problem -- showers that make an annoying high-pitched squeal when you run the water -- but you can probably fix it yourself.
In this video from This Old House, we learn that the squeal is often caused when water is trying to fit through a tighter space, going from a wide pipe to something with a suddenly smaller aperture.
Amusingly, Richard Trethewey misdiagnoses the problem at first. The most likely culprit was the mixing valve cartridge that controls the flow of hot and cold water. That's what they spend the bulk of the segment replacing, and it might be the source of your own singing shower. It's fairly easy to replace without a professional plumber; the specific parts you'll need will vary depending on the brand of plumbing fixtures in your shower, but as long as it's something contemporary, it shouldn't take too much work to find replacement parts online. But it turns out that wasn't the source of the problem in this case.
His next guess was the shower head -- another place where water flow is suddenly constricted. Nope. Turns out the culprit was the diverter tub spout -- that little knob you lift to direct the flow of water from the tub spout to the shower. The lesson here is that those annoying noises are caused by the small spouts and mechanisms vulnerable to vibrations. Chances are your shower is squealing from one of those three sources.
How to Repair a Squealing Shower [This Old House via YouTube]