Changed circ.breaker-vocals became shouty:why?

Don't put a 30 amp breaker in a 15 amp circut !! that is a fire waiting to happen. For a 30 amp breaker you need 10 gage wire. If you wire is less then 10 gage the wire burn up before the breaker ever trips. Get a new 15 amp breaker and try your tests again.
It is an intersting expermint though, After you replace it with the correct size, run it for a few weeks and see what happens, Then switch it back and see what difference you hear.

Mark

You can't just swap a 15 amp breaker with a 30 amp. It takes special wire and outlet plugs for 30 amps. If you have a short you could burn the apartment down.

With that said, there is a break in period of 2 weeks on a breaker but the difference you are hearing sounds like it may involve more factors.

Breakers do sound different but the better ones are mercury wetted. Another thing that makes a difference is if the copper thickness or length in the new breaker is equal to the wave length of something causing interference.

You can play around as long as your hardware store lets you return items but I would go back to a 15 to 20 amp breaker.

The vocalists are trying to warn you that your house may burn down! You can't just insert a 30 amp breaker in place of a 15 amp one. The rating of the breaker depends on the wire that it feeds into. A 30 amp breaker has the same resistance as a 15 amp one and, unless you believe in magic, has no effect on the audio signal. Either breaker will deliver the current that your audio system demands, and you can't make the audio system demand more by changing the breaker.

The 30 amp breaker would permit you to plug in a TV and an Airconditioner as well as your audio system, and a few other things, without the breaker opening. The wires will get hot, and even if you don't start a fire right away the insulation of the wires will be damaged, which is a long-term hazard.

What is the size of the wire between your outlet and breaker?

Ignoring your question, but you can't just up the amperage of the breaker unless you've upgraded all of the downstream wiring in the walls to match. Big fire hazard if you don't.

No idea why the sound would change.