Yes, parallel the 0.1µF cap across the 1M resistor (input to ground). It shunts RF noise while letting audio through—1M blocks DC/low freq, cap handles highs. Start small; too big caps kill treble. Measure impedance if picky.
Discussion
Start with .1ufd and work up in value? I could use some slight reduced treble anyway. How high of a capitalist before I can say this was unsuccessful.