Why does my Mesa TA 30 play One note in 3 octaves?

My Mesa Boogie TA30 112 Combo has fresh power tubes from 6 months.

My problem is that when I play a single note, the amp's sound resembles an "Octave Divider". You actually hear 3 notes. It strangely sounds like the octave above, and the octave below, as well as the original note, totaling 3. Strange as it sounds, but true and I have audio to prove my sanity.

Any suggestions?