My flight from BOI-SEA (QX2363) got interesting over the Cascades last night (7:30pm departure). We were humming along when the starboard engine started to get a bit of a resonant vibration to it. Shortly after, that I heard something that sounded like something had fallen to the floor in the lav. Didn't think too much of it as the props on the Q400 are variable pitch and the flight crew had just come on the intercom about 10 minutes earlier saying that ATC had slowed our approach due to several planes stacking up.

After a minute or two of the vibration and sounds, the pilot gets on the intercom again and says the sounds/noises we are hearing is the de-icing system doing it's job. So those were ice chunks coming off the props and striking the A/C. Also, when you had ice on some props and not others, the imbalance caused the vibration. I bought the story and went back to reading.

The interesting thing is that I've been making these trips back and forth over the Cascades (SEA-GEG) for about four years now and had never run into that scenario. Has any of the FTers out there run up against this before? Made for an interesting flight.