Have a fender passport thats cutting in and out a lot.

[andrew58]

When ever my vocalist really gets into it and gets loud, his voice pops in and out quickly. He is not clipping either it just starts doing this when ever it gets to maybe 4/5 of the way to clipping. I know my way around amps enough to get me by. I'v fixed tube amps and solid state guitar amps and rack-mounts. like the cs models and qsc's stuff so i could use a bit of technical advice. And by no means am i an expert i have just learned things through the years to help save money on repairs of broken and blown gear.
I don't think its going into protect or anything, i had some one mention that to me the other day, it just makes a popping sound of you coming on and off and on quickly and randomly when you sing a long loud note. ALso i believe its the newer model black cased passport not the grey one i believe. we just started using it about two weeks ago. I didn't buy it new either so there is no warranty.
Thanks for your help.