I can't even believe I'm responding to this. :3d_frown:
The only way to make a turbo spin 'backward' is to have air flowing backward. The turbo does not go 100k rpm to 0, the turbo is trying to spin forward, but air is forced back while the turbo is still spinning the air forward. This causes the 'chuffing' sound - air pressure builds up, forces past the turbo, and the turbo continues to spin, causing, again, the chuffing. The reason this is so hard on the bearings, is because of the pressure wave running directly across the compressor.