Video banding /pixellation audio OK

2) I am using Panasonic AY-DVM63 MQ Master DV tapes in XL1. I have never used other than Panasonic, although the Master part is new. Two out of 5 tapes were fine on audio, but pixellating, banding and dropping out. I ran the same tape back through the camera right after the bad footage and the image was fine. I even taped over the offensive footage and it was clean. It's almost as if there is electronic interference. The two locations were cities apart.