It is due to the characteristic of the microwave oven that the heating begins at the internal of the meat. A popping sound is normal for foods with high fat, the reason for it is that the water and oil inside are vaporized by heat but the steam cannot be released because of the fat and skin outside.
Therefore, when heating foods with high oil or fat content, please use the special plastic wrap designed for the microwave oven to cover the food and tie some small holes, or add the microwave oven lid to prevent the oil from contaminating the cavity of the microwave oven when it bursts.
Besides, after each use, wipe away any food or grease splatters inside the oven to clean and maintain, otherwise there will be some damage to the microwave oven over time.