We were looking into the problem and realized it was not a
problem at all. The only thing you will need to do to get rid
of that sound is push the “Hum reduction” button right on the
front panel. This acts as a noise filter and it is just
responding as “on off on off on off” in those certain frequency
ranges. That is the tremolo sound you are hearing. When we hit
>the “Hum Reduction” button, the tremolo sound went away.