Accentra insert auger noise?

i have been burning my new-to-me 2006 Accentra insert for a couple of weeks now and it has been working great. But last night it started to make a faint but definitely audible noise intermittently when the auger feeds. It's kind of a whistling or squealing sound, almost like if the wind were howling outside in the distance. It doesn't happen all the time that the auger is feeding, just intermittently. Has anyone experienced this, and if so is there a fix? I'm hoping that maybe it will go away after I shut the stove down later today and let it cool down.

Thanks for the suggestions, I did a hot burn and tried to scrape the opening area of the auger tube and the noise seems to have gone away. After doing some more research on this forum I see that this is a fairly common issue with Harman stoves. Seems like carbon build up is the most common cause, along with fines build up in the hopper chute and fines collection box. One guy claims the problem can be permanently fixed by removing the auger and adding some spot welds to better fasten the spiral to the shaft, thereby preventing the harmonic vibrations that cause these noises. Maybe I'll try it next spring.