What's with the converter?

Question

Rechargeable batteries

I assembled a circuit: 3 AAA batteries, a DC-DC voltage converter, a switch and a load in the form of a telephone.
When a phone is connected, the transducer starts making a pisco-like sound. Voltage 5v, current 0.6 A.
What kind of sound, what's the problem?

Answer 1

It can squeak for a variety of reasons. Offhand:
- transformer windings squeak, if any;
- squeak throttles;
- squeak capacitors;
- the transducer itself beeps, because its frequency is in the range of audible frequencies.