Hi. I bought my MB150E-III head and an MBX112 cab about a month ago. It sounds fantastic with my YamahaTRB-5 and all other basses I plugged in, but I found that there is noticable background hiss, the hiss from the amp, not the bass (I tried to lower the preamp/master volume, then disconnected the cord, but the hiss remained). In fact, the hiss is not very loud, I can hear it only when I stop playing, but it exists. Is it common with these amps?