Irish band. At last gig, the penny whistle and accordian became unplayable in high registers as the board added overtones and made these instruments sound like they were gargling. Other instruments and vocals were fine. Turned off all effects, compressors, gates, etc but no change. Playing into mic wired to Rm mixer as stagebox and then to SL 24 via Ethernet. Sound is fine at headphone out of RM. This setup has been fine for a long time but suddenly adds strange effects to these instruments and only when played in high registers. Any ideas how I should troubleshoot this?