I hear it only in Netflix from time to time.
If I hear it twice in a few minutes, I exit Netflix & return...this usually fixes the problem.
Roku Stick: 3800RW
Roku Stick: 3800X
Roku Stick: 3600X (Died)
Roku 1 SE: 2710X (Retired)
Roku 2 XS: 3100X (Retired)