low flying silent aircraft also reduces noise of heavy traffic

I don’t think this was a ufo, but rather some secret VERY quiet aircraft of some sort that passed near overhead at around 5:35 pm.  (Dec 10. '17 ) heading  northwest.   
I went outside to grab a smoke, and almost immediately I saw off to the north east a craft rather low but seemed much larger then a Cessna and this made me curious about it, and I listen for the engine noise, NONE!  No sooner then that I began to feel a pressure wave in cycles ( about 2 per sec ) but NO NOISE,  and here’s where it got strange, I live 300 yards from a major highway and the sound from the traffic also was muffled during these cycles …. Quiet – then normal –quiet – normal repeatedly, I could feel a pressure on my ear drums very similar to going deep in a swimming pool, the same kind of pressure the same deadening of sound….. I estimate that the sound of the highway traffic dropped by 80% during these cycles so it was very evident this craft was doing something to cause it.
I watched the aircraft head away with my ears paying close attention to the traffic noise and after the craft was ¼ ~ ½  mile away  the normal traffic noise returned and the pressure on the ear drums went away.
Its speed was that of a Cessna, but there was enough visual indicters showing that this was larger, a helicopter of some sort,  Drone?