Hi there - I have an AS50D acoustic amp, and whenever I turn the volume up past about 1/3, it consistently makes a loud "pop" sound when I strum.  I have tried muliple instruments, multiple cables, and multiple rooms/power sources with the same result.  I have also trued both channels and with/without a mic in channel two.  All the same result.  Presently I can't use it because of this.  Please help, it's less than a year old!

-Nick