Whether I plug my guitar directly into my Mac or mixer I pick up a signal that is hear the program material from a radio station broadcast. Please tell me. How can I stop this annoying and incessant interference? Thank You for your helpa

 

Take up drums?

 

Ferrite beads on the phono cable or better shielded cables. Or take up drums.

 

Look for pi filters if the ferrite beads don't work.