Stray current through my audio rack???

If you have an AC volt meter touch one test probe to the ground hole contact of your wall electrical outlet, the other test probe to the metal audio rack. Post back with your findings.

If you have no meter, unplug everything on the rack or flip your breaker. See if the tingling stops.

attach a basic #18awg stranded grounding wire, connecting the rack to a nearby AC outlet ground. Attach the grounding end of the wire to outlet cover-mounting center screw. Use a hose clamp to secure the other bared end to your rack post. This should cure your tickles of any leaking stray voltage from a component. But if it does then you should attempt to invert the AC input plug polarity of the offending device, then test again. Stray AC leakage can result in serious repurcussions to your safety so do be careful.