I have a furnace that started whistling, recently.
I have adjusted the pilot adjustment screw, in an attempt to change the amount of gas flowing through the pilot. 180 degrees turn in either direction did not cause any observable change in the gas flow (size of he flame). The 'whistling' persisted evenly through that change.
What else can cause a pilot to whistle? Or, perhaps, is the matter likely that I need to adjust the pilot screw farther than I did?