High pitched noise while burning?

[VLC18]

I was doing some burning with my 1w 445nm laser and I noticed something.every time I would put the focal point on something I would hear a very high pitched noise. Does anyone know why this is?

 

[julianthedragon]

What were you burning?

 

[CurtisOliver]

I've noticed this phenomena on coated steel before.
My best guess is that for best results it has something to do with laser pulsing and laser intensity. Fibre laser engravers can also produce sound on metals and certain plastic materials depending on their frequency and pulse width.
I can confirm that when I observed the phenomena, the sound originated at the material. Not the laser itself. So internal electronics wasn't responsible for the buzzing sound. It sounds like it has something to do with the photoacoustic effect.

 

[VLC18]

What were you burning?

Wood

 

[kecked]

Steam…..sap….some other volatile. When wood burns it releases gases which expand.