Hello Mark and welcome to the Cow Audio Forum.
The A&H 24 channel mixer has no preamps? What model is that?
I'd begin by suspecting the mic and the mic cable and go right on down the line from there.
Yes, do post a sound sample.
Regards,
Ty Ford
Audio Forum Leader

Want better production audio?:
Ty Ford's Audio Bootcamp Field Guide
Ty Ford Blog:
Ty Ford's Blog