I seem to get a farting noise when I play low A, B or C. I have the Ultra LO button on(+2.5@50HZ), the bass at 9 o'clock(about -6), but the bass(40HZ) on my ZON half way past center. I also have the graphic EQ on, but the 30HZ slider all the way down. Doing this helps a bit, but there is still farting. Also, I run the bass in the passive style input, not the -15. Does anyone know the tuning frequency of this cab? Am I putting too many low frequencies into it? Also, can I use the biamp feature with one cab to cut all the frequencies below 50HZ? Thanks in advance.