the "beating" noise was mainly known from propeller planes but can also appear on jet engines (but less in terms of sound pressure).
it is caused by the fact that the props or the fans of the negines are not exactly turning at the same speed. since the sound emitted at the prop or fan is - in terms of frequency and level - a function of it's runnig speed, the individual spped gives an individual sound. when the sound of two engines comes close together in terms of frequency, the "beating" phenomena installs, it is the perception at ear level of the different sound individuals with frequency variations. it's very incomfortable, but wil not impact the structure of neither the engine nor the aircraft.
in the golden days of prop flying, the flight engineer spent some good time of the flight adjusting the throttles individually to illiminate the beating. two possibilities exist: either you trim the engines to run at exactly the same speed, or you offset the engine setting that much that the frequencies cannot overlap between the engines ...
high sound pressures from any source close enough can impact structure life. the technical term is sonic fatigue, and the design usually takes care for that.