converted furnace harmonics
 

My Sears furnace, converted from NG to LPG, during warmup, produces harmonics similar to a trombone, and the noise subsides after ~30 seconds.
What causes this musical phenomenon?
Thanks.

Could be low gas pressure to the furnace.
Or the gas valve itself.

Interestingly. It's similar to a window a/c unit. If there's too much of a voltage drop (undervoltage) for any reason, it will rattle the frame until it reaches full operating capacity (in terms of running RPM.):huh:!

Something like that.

Take a soda bottle. Blow across it. And it makes noise. If the pressure is too low going through the valve, it can sign a little.

Thanks, and I think(and hope) that's exactly what's happening: low pressure from the supply to the valve, and even lower pressure from the valve to the furnace, which I think will become quieter when I get the correct supply, to the correct valve.