It is a sad thing you cannot 'unhear'.
It reinforces why planes, large and small, always strive to steer clear of precipitation, particularly thunderstorms.
This plane was going though turbulence that was bouncing them in 700' cycles.
Thunderstorms can have major locallized vertical winds than can shear planes that might pass the boundary zones.
And the up drafts can drive the tops of these storms higher than a lot of other precipitation that you can pretty much fly over in a jet.
The up drafts can also bring water droplets with it, so you can be in way cold high altitude, and bang, all of a sudden you have wing icing.
NTSB will be final arbitter, but I bet all of the above factors come into play here.