Not sure how efficient your M&Ks are, but if they're power hungry and the distortion is only coming from peak volume swings like the screaming you described, it could be distortion that resulted from driving the 7100 into clipping.

Once the waveform "clips" it generates high frequency harmonics that we hear as a brightness or harshness that is abrasive or downright painful to listen to. These harmonics also deliver a lot of power to the drivers which can cause them to blow. Like happend to me!

As to the pop, not sure what that could be. Are you powering up your amp before or after the 970?