How would I have an AI Target areas where a noise is made?

That's a simple way to do it.

If you simply keep track of all of the "sounds" made in the last few seconds, the zombies can track to those instead of the nearest player. If there are no nearby positions to take, just remember the old value, so that it'll keep tracking there (and you can add additional logic to make it wander).

Overall, it could look like this:

function makeNoise(position)
	local p = Instance.new("Vector3Value",workspace.Noises);
	p.Value = position;
	delay(function() p:Destroy(); end,10);
	-- Destroy the noise after ten seconds
	-- (since zombies might not look every moment, we give them
	-- a chance to notice)
end


function findNoise(near,within)
	local nearest = nil;
	for i,v in pairs(workspace.Noises:GetChildren()) do
		if (not nearest) or (nearest - near).magnitude
			>
		(nearest - v.Value).magnitude then
			nearest = v.Value;
		end
	end
	return nearest;
end

local target = myposition;
local vary = Vector3.new();
while true do
	wait();
	-- Other logic
	local noise = findNoise(myposition);
	if noise then
		target = noise;
	end
	if math.random() < .01 then
		vary = Vector3.new(math.random()*50-25,0,math.random()*50-25);
		--simple wandering
	end
	wandertarget = target + vary;
	moveTo(wandertarget);
end