The shaking bit comes from the QRH description of one of the clues to identify a severe damage just as the 'engine' vibration clue is used to help in identifying an engine stall/surge...
engine certification (CFM flight ops support)
Overtemperature test
Demonstrate, by engine test, the ability to operate for 5
minutes at 42°C / 75°F above declared limit (N1, N2 at red
line) with post-test inspection showing engines parts within
serviceable limits.