Startup Buzzer Sound
Figure 1. The ULN2003 internals.

The first thing to jump out of your schematic in that area is that you haven't connected the COM to your +12 V correctly. Your schematic shows it connected through a switch to ground.







simulate this circuit &ndash; Schematic created using CircuitLab

Figure 2. Representing the transistors as switches. (a) The correct wiring. (b) What you have done.

The diodes in the chip are there to prevent the transistors from damage when switching inductive loads. They should be connected to supply positive.

Looking at Figure 1b, your setup, it should be clear that if TEST is closed that current will flow from +12, through the buzzer, through D3 and through TEST to ground. The circuit will be completed and BUZZ will buzz if TEST is closed.