Originally Posted by msbbarratt
I've sometimes noticed as a passenger the inter engine beating during and shortly after takeoff, but thankfully it always seems to disappear when cruise speed and height is reached.
That's because EPR is king during takeoff, at least on my Autothrottle machine. For takeoff, EPR is set by the system, not the N1s. If one engine was a little "better" than the other, it's N1 would be less and so you'll get out-of-sync harmonics/beating. At climb and cruise power however, N1 is king; one engine is picked as the master and the other is slaved to it using N1 as the slaving parameter = no beating.