Did you check the power supply? Did you check the noise to see if it is regular/periodic, or random? Did you turn off all the lights to see if the noise was affected? Did you use shielded wire for all the audio connections, with only ONE ended grounded to the Arduino? Do all the ground connections terminate at a single point? Are the signal wires kept far away from any power wires?
Lots to do if any answer is no.
Paul