Mk134 Whistle Changing Pitch

I was testing my Mk134 kit and the whistle suddenly started to change to a high pitch squeal and now has a sort of tremolo effects.

What could this be?


Is the unit still producing ‘steam engine’-noises ?
If not, either the voltage doubling part (IC1C) or the noise generating part (IC1B) of the circuit is not functioning correctly, or the battery is simply too weak…

Yes,it still does produce the “steam engine sound”

Then I’m afraid at this time, we have no idea what might be wrong.
Make sure a mechanical problem is not at the cause of troubles (bad/loose solderings, broken track/pad etc…).

It doesn’t seem to be changing pitch now.