Possible Clues:

• Lines crossing circles in harmonious combinations
• Guitar-lesson diagrams
• Guitar-book diagrams
• Similar to those at the end of 22 across in short pants, so to speak
• Guitar Hero combinations
• Medic cuts hours short and gets around to piles of notes upon notes, perhaps.
• Musical combos?
• Many pop songs use the same four
• G, D and E, at guitar lessons
• Groups of musical notes