Since both the faucets and the toilet trigger the noise, I’d check the house water pressure first. If water hammer is the cause, an arrester close to the worst offending fixture is the lasting fix. Draining the pipes usually helps only temporarily.

Older plumbing sometimes has capped pipe sections that hold air to cushion sudden pressure changes. Draining can restore that air cushion, but the air gradually dissolves into the water. Your brief improvement fits that explanation, though it doesn’t prove your plumbing has those chambers. Modern arresters separate the air cushion from the water so they don’t become waterlogged. [Sioux Chief explanation](https://www.siouxchief.com/Products/SuperDetails/19)

1. Measure the water pressure with all fixtures off. Attach a hose-thread pressure gauge to a hose bib supplied by the same regulated plumbing as the house. If the reading exceeds 80 psi (about 5.5 bar), address the pressure regulator first. Partially closing the main shutoff reduces flow, but it won’t reduce the pressure when everything is off. [Watts pressure guidance](https://www.watts.com/resources/references-tools/waterpressurereducingvalvesfaq)

2. Check whether the noise is water hammer or valve chatter. Try closing a faucet slowly, then quickly. Noise mainly after a quick closure points toward water hammer. Buzzing or rapid vibration as the toilet finishes filling can also come from the fill valve or supply shutoff valve. If one toilet causes most of the noise, cleaning or replacing its fill valve according to the manufacturer’s instructions is a reasonable DIY step. [Fluidmaster’s noise guide](https://www.fluidmasteruk.com/sounds-of-the-cistern-system-what-do-they-mean/)

3. If you confirm water hammer, fit an arrester near the valve causing it. Screw-on models can fit between a fixture’s shutoff valve and flexible supply hose, often without cutting pipe. Choose one with the correct connections and follow its placement instructions. Shut off the supply and relieve the pressure before disconnecting anything, then check carefully for leaks afterward. An arrester at the main inlet may do little for a distant fixture. [Arrester placement and operation](https://www.siouxchief.com/Products/SuperDetails/19)

4. Check accessible pipe supports. Loose pipes can make the noise louder by striking framing. Secure them with supports suitable for the pipe material, without overtightening.