Beep; Flicker Reduction - Nikon D3400 Reference Manual

Beep

Choose the pitch (High or Low) of the beep that sounds when
the camera focuses and in self-timer and remote-control modes.
Select Off to prevent the beep from sounding.
The current setting is shown in the
information display: 3 is displayed when
the beep is on, 2 when it is off.

Flicker Reduction

Reduce flicker and banding when shooting under fluorescent or
mercury-vapor lighting during live view (0 39) or movie
recording (0 138). Choose Auto to allow the camera to
automatically choose the correct frequency, or manually match
the frequency to that of the local AC power supply.
A
Flicker Reduction
If Auto fails to produce the desired results and you are unsure as to the
frequency of the local power supply, test both 50 and 60 Hz options
and choose the one that produces the best results. Flicker reduction
may not produce the desired results if the subject is very bright, in
which case you should select mode A or M and choose a smaller
aperture (higher f-number) before starting live view. Note that flicker
reduction is not available when On is selected for Movie settings >
Manual movie settings (0 142) in mode M.
G button ➜ B setup menu
G button ➜ B setup menu
B The Setup Menu: Camera Setup
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