How does the shutdown feature for MAX9722A work?

Thank you for your interest in the MAX9722A.  I've reviewed the conditions and had a few basic checks done in the lab. Placing the MAX9722A in SHDN will allow for low current consumption and place the outputs in high-impedance mode (10kΩ).  As you surmised, there is no active mute and that is not possible since there are external resistors to the MAX9722A.  As a result, there is an external pathway for some amount of signal to pass from the input to the output.  There should be significant attenuation on this of at least 60dB.  However, that may not be enough to completely mute a headphone set.  While in SHDN, RF+RG act as a resistor with the output load. You should be able to increase the output attenuation by increasing RF & RG while keeping the desired gain.

The best solution would be to disable the input signal when placing the MAX9722A in SHDN mode.

Hi Mike,

Thanks for testing this for me.

Yes, I figured it might have been "leaking" through the gain setting resistors.
My solution will be to disable the input whenever the SHDN pin is set low as you suggested.