My guess would you be either you are breaking simple rule, and putting the microphone in front of a speaker; OR there is a frequency that is being excited. If you don't have the microphone pointed near the speaker, then I would suggest using an EQ either one built in the instrument (if that is a feature) or an external EQ. If you are using the built in speakers of the instrument make sure the mircrophone is a hyper-cardiod and you don't have the mic on an angle. Have the mic end (where the cable is plugged in) pointed directly at the speakers.

[This message has been edited by PaulD (edited 02-11-2003).]