Hissy audio
 

It appears that by setting your SVM to -10 youre causing the hiss to appear by the pre-amps in the camera to gain up to make up for the gain difference.

I, too, believe the "hiss" is a noise from the camera's preamp amplifying the weakened input from the mic as the result of the -10 dB setting. Again you will definitely have more background noise in place of that hiss if the switch is set to 0 dB.

There is no getting around this problem unless you obey the law of physics by getting the mic close to the source. If the sound source is more than one as in your case you have to compromise by either positioning your mic not one or two feet from the singer but finding the "optimum sound spot" in the room and living with some degree of background noise or asking for a direct audio feed from the band/club.