Mercury Black Max 200 efi ticking noise

[bftr]

1993 Merc Black Max 200 efi. "Ticking" noise subtle and most noticeable around idle. With stethoscope, targeted on the "brain" side (starboard) just behind the lowest cylinder. No power loss, 95+ compression all cylinders. Lower unit solid. Checked for exhaust leak, spark jump ... all negative. IMAO (amateur opinion) tick sounds mechanical. Before a power head tear-down, have any thoughts?