Hi. I have calibrated my system using S&V disc and Radioshack SPL meter several times since I change the positioning of the speakers quiet a lot. After adding a sub, I saw that the S&V disc's subwoofer level tone, which plays in turn with the left front, makes the left front woofer pop. I mean when the signal passes to the sub from the left front, there shouldn't be anything heard from the left front but I hear a constant "pop-popop-pop..." like sound. Has anyone else experienced this? Is it normal? Since calibfration needs high volume, I wonder if this situation has any damage potential to the speaker. I have Kef Q35.2's by the way, they are 91db 100W, 42 or 45 hz lower freq. response. TIA.