For a long time now there has been this faint pulsing noise in the headsets when serial data has been enabled on our Garmin 696. I tried so many things to get rid of the noise and FINALLY I fixed it. After having tried double/triple checking all grounds, adding a 'noise filter', re-crimping wires, replacing music jack cable, and probably other things, the solution was to add a 1k resistor on the blue serial data line. I read an old thread on VAF where someone had suggested this to someone else and I was so relieved when it worked!