What causes this horrific loud "blast" sound when the faucet is turned on

Whenever the people living in the apartment directly above mine turn on their bathtub faucet there is a tremendously loud blast like a hissing whoosh blast sound of the titanic sinking. It lasts for a few seconds and then fades away into a dull hum. It is so shocking that my heart skips a beat everytime the relative quiet of my life is interrupted by this blast. What accounts for this noise? air in the pipes or something? Is it possible to insulate the pipes to make this sound quieter? This is an old apartment complex and the plumbing is not that great. Please help.

When I lived in a pre-war apartment building in Queens this sort of thing happened. I’m fairly certain it’s air in the pipes. Basically, old plumbing systems tend to deteriorate and holes can form.

This is really bad, BTW, since that means that the water may well be polluted. The tap water in our apartment was so bad, we wouldn’t drink it even after boiling it.

Hate to tell ya, but if you had holes in your pipes it would shoot water out, not let air in.

I’m guessing that it’s air in the shower leg of the pipe. After the faucet valve, there is the diverter that will send the water up to the shower nozzle. After the water is turned off, the water will leak through the diverter (or just run out if the diverter is opened).

If they don’t have a low flow shower head, the water rushing up the pipe will displace the air, which will whoosh out, then when the water hits the head and the flow changes, you’ll get water hammer (the bang).

If they replace the showerhead with a modern water saving head, this may be somewhat minimized.

Just my guess.

Other than that, I’m not sure what makes some pipes louder than others.

Insulation may work, but the pipes themselves may be impossible to get to without going through drywall/plaster.

The phenomenon you mention is called a “water hammer”.