Artifacts while using pitch shift of +24 (fine with +12)

I recorded our band (direct from the desk) over the weekend & I noticed that the recording (guitar direct via Kemper out) was Clean & void of artifacts, where as my amp was sounding nasty with digital noise while using the whammy/+24 pitch shift. The whole band noticed it on stage. Is my guitar amp (for monitoring) not handling the extra frequency range perhaps or is there a setting for the monitor out I should change?? Thanx