Sawdust smell coming from Mitsubishi mini split

Have an odd situation where we are getting a mild-to-moderate whiff of sawdust coming from two of the three mini split heads attached to our Mitsubishi hyper heat unit. It started a few days ago and since then we've had a tech come check it out and clean them. They too noticed the smell, which is most apparent when the units are on standby and the blower is running slowly. Units are currently set to heat and have been running all winter long without issue. The tech escalated the issue to Mitsubishi and are coming back out on Monday, but does anyone have an idea as to what could be going on?