Diagnosis
That's the sound of a dry bearing on one of the fan wheels (usually the main circulation fan for the heat pump system), or less commonly, a foreign object touching the fan blades.
How to Fix It
- Unplug the dryer and pull it out.
- Remove the rear service panel (several Torx screws).
- Inspect the large black plastic radial fan (the circulation fan) for any debris like a sock, coin, or lint clump caught in the blades. Remove it.
- Manually spin the fan. If it spins freely but the noise persists when you spin it, or if it feels gritty, the bearing in its motor is failing and the fan/motor assembly needs replacement.
If That Didn't Work
The noise could be from the smaller fan on the compressor itself. This is a more involved repair, as it's part of the sealed refrigerant system's external cooling.
Heads Up
Don't run the dryer with this noise. A failing bearing can seize, which can burn out the fan motor or cause the overheated fan to melt its housing, leading to a much costlier repair.