Is the noise coming from the back of the appliance near the compressor?
It seems to be yes.
Ok if it is then its possibley a faulty condenser fan. Pull the freezer out if you can and remove the back panel.
From there you will see the condenser fan next to the compressor. Just check theres nothing touching it that's causing the noise. If its all clear and the noise is the fan then it will need to be replaced.
As to the ideal temp for the freezer its about -18 degs.
If you need anymore info just get back to me.