Squealing and whistling sounds from the pipes in your home can be caused by a variety of different problems, from water pressure that needs adjusting to drain vents that need to be unclogged. Because the causes can vary and aren't always easy to diagnose, the quickest way to fix this annoying problem and avoid any damage is to have a professional inspect your plumbing system.
Water Pressure Is Too High
A common cause for squealing noises is water pressure that's too high. When too much water is being forced through pipes that aren't big enough to accommodate it, it can cause the pipes to make this sound.
If your home's water pressure is higher than it should be, it could point to a faulty water pressure regulator. It's also possible that your water pressure is within the typical range but may still need to be adjusted. Contact a plumber to have your water pressure inspected.
Pipes Are Rusting or Corroding
If your water pressure is fine, the problem could also be resulting from old pipes that are rusting or corroding. Rust and corrosion can reduce the volume of water pipes can hold, and they can also start to leak or break. Squealing and whistling sounds can often be a sign of, or a precursor to, damage to your pipes that need immediate attention.
Toilet Assembly Needs Replacing
If the squealing sounds are coming from your toilet, the problem might not actually be in your pipes, but in the toilet assembly itself. This can especially be the case in older toilets where the parts inside the tank haven't been maintained or replaced in years. Specifically, the problem can come from a faulty or worn-out washer, which will no longer provide a water-tight seal, and can result in loud noises when water passes through.
This can sometimes be fixed by replacing just the washer, but if the problem is persistent, or if the parts are all very old, the entire internal assembly should be replaced.
Drain Vents Are Clogged
Your drain vents are responsible for regulating air pressure inside your pipes, and if they're clogged, liquid won't be able to flow properly. If the vents are clogged, water can drain very slowly even if the pipes are clear. It can also affect incoming water as well, which can be why your pipes emit a squealing sound if you're taking a shower or running the washing machine.
The fix for this is to simply have your vents unclogged. If you suspect this may be the problem, contact a plumber to have your vents inspected and cleared.