Random "attempt to index nil with 'GetDescendents' errors? [SOLVED]

Title says it all, I am trying to setup sound regions and make it so that the sounds fade in or out realistically, however this has proven to be a real pain.

Basically, sometimes when I launch the game the script works as intended, other times though, it'll throw this error and it won't work.

Here is the code in question.

-- [ TODO: FIX LAG ] --
-- [ stops and starts regional sounds with fading in and out ] --
-- [ DO NOT MAKE A SOUND WITH ANY VOLUME OTHER THAN 0, THIS SCRIPT WILL MANAGE THAT ]

-- get sound service
local sounds = game:GetService("SoundService")

-- get sound regions (area where sounds are played)
local sound_regions = workspace.SpecialBrushes:WaitForChild("SoundRegions")

-- detect if player is in zone
local found = false
local player = game.Players.LocalPlayer

while wait() do
	-- do this for each individual region
	for i, v in pairs(sound_regions:GetChildren()) do
		found = false
		
		-- create region from 2 points
		local region = Region3.new(v.Position - (v.Size/2), v.Position + (v.Size/2))
		
		-- find parts of user that are in region
		local parts = workspace:FindPartsInRegion3WithWhiteList(region, player.Character:GetDescendants())
		
		-- go through everything in parts table
		for _, part in pairs(parts) do
			if part:FindFirstAncestor(player.Name) then
				found = true
				break
			else
				found = false
			end
		end
		
		-- play audio, target audio is 0.3
		if found == true then
			if sounds.Ambience[v.Name].isPlaying == false then
				sounds.Ambience[v.Name]:Play()
				
				-- fade out
				for count = 0, 300, 1 do
					sounds.Ambience[v.Name].Volume += 0.001
					wait(0.0001)
				end
				break
			end
		else
			if sounds.Ambience[v.Name].isPlaying == true then
				-- fade in
				for count = 0, 300, 1 do
					sounds.Ambience[v.Name].Volume -= 0.001
					wait(0.0001)
				end

				sounds.Ambience[v.Name]:Stop()
			end
		end
	end
end

Help would be much appreciated, and I apologize in advance for any newbie errors I may have made as it's been a while since I scripted on ROBLOX.

EDIT: ANSWER BELOW

Thanks to T3_MasterGamer I found out that no, you should not put something like this in the StarterPlayerScripts, and that a more appropriate place to put it would be in StarterGui or StarterPack, I myself chose StarterPack as I feel like that fits it more, but you could also choose StarterGui.