Regency H2100M Hearth Heater whistling noise from 'hole'

[gmcinnes]

Hi:

I have a Regency H2100M hearth heater that I got around 2018.

There is a draft rod on the left. And beside that draft rod there is a 1/2" hole.

Once I have a fire at about 500F established I close the draft rod about halfway. The odd thing is is that the hole then begins to whistle. If I open the draft rod again it stops. Where the whistling starts and stops is proportional to the size of the fire in the firebox. As the load of logs burns down it doesn't whistle with the draft rod at halfway, but starts again if I happen to close it further.

The whistling is not mentioned in the manual, but is it intentional and trying to tell me something, or just a quirk of that design?

(Right now I defeat the whistling by balancing a small splinter in the hole. It's small enough that it has negligible effect on the volume of air passing through, but increases its turbulence, preventing the whistle.)

What gives?

 

[DAKSY]

If you check the inner & outer edges of that hole, you may find that it was not correctly de-burred from the factory. Take a small rat tail file & see if you can remove any sharp edges. If that doesn’t cure it, a small rare earth magnet works to cover all or part of it.

 

[gmcinnes]

Thanks. I searched for this topic before and didn't find anything, but now there's a good list of similar threads below this post

I guess my remaining question is: what is that hole for? Is it to prevent a user stopping *any* air entry?