A:Answer that would be the magnetron engaging. The most failed part in todays microwaves. On start, It takes a few sec to purge the radiation or less stress on the unit, then produces the load noise of the 1100 watts. Also, prior to the unit timer counting last seconds down, the noise with stop to help reduce radiation. So, normal for mine to repeatably do this noise thing (sounds like the electricity load has lifted now the 1100 watts inst making noise) Just remember abruptly door opening during cooking radiation comes out of the cooking field at you.