Play ambient noise with random sounds in the background. Sounds different every time you play it.

noise.sh

#!/bin/bash

# Ambient background noise with randomized sounds.

# You can get suitable sounds from freesound.org, BBC SFX library, and other places.

whitenoise="white-noise.ogg"
soundsdir="sounds"

if [ ! -e "${whitenoise}" ]
then
    echo "White noise '${whitenoise}' not found."
    exit 1
fi

if [ ! -d "${soundsdir}" ]
then
    echo "Soundsdir '${soundsdir}' not found."
    exit 1
fi

# Permanent background noise:
mpv --quiet --loop-playlist "${whitenoise}" &
whitenoisepid=$!

# Generate random silence between tracks:
# (has to be in a subdir of soundsdir, because mpv --shuffle dir1/ dir2/ does not expand dir2/)
if [ ! -d "${soundsdir}/silence" ]
then
    echo "Generating random silence in '${soundsdir}/silence'..."
    mkdir "${soundsdir}"/silence &&
    for i in $(seq 100)
    do
        sox --null --comment="" "${soundsdir}/silence/silence-${i}.ogg" trim 0.0 $((SRANDOM%60)).$((SRANDOM))
    done
fi

# Four channels of random sound effects (bird, rain, silence, wind, cricket, ...)
(
    for i in $(seq 4)
    do
        sleep 0.$RANDOM && # mpv sometimes uses the same random seed
        mpv --quiet --shuffle "${soundsdir}/" &
    done

    wait # for mpv sounds
)

# All sounds played. Stop the white noise.
kill "${whitenoisepid}"