I am only posting a idea on this one. I have heard flames make many strange noises when the air/mixture is wrong. A flame can whistle, or rumble I wouldd guess if it is connected to the having to bleed the system that it would be a lean flame? they tend to run at higher temps that could break up the water near the surface. I hope this may give you a idea. What does the flame look like and what type of fuel is it using?