More then likely it's the condensor motor fan and it's either bent or clogged do a visual inspection of it. Also this is a very fragile item if you clean it clean it very gently with a small paintbrush and do not touch the fan blade at all by hand if you can avoid it, the blades are made super cheap and bend easily causing the noise. If you find it's the condensor motor fan just replace the blade, looks like you can just order the fan blade by itself and try it. If the fan blade itself doesn't do the trick and you know it's coming from that then you'll have to replace the fan motor as well if the shaft is bent or out of balance and that runs for around 120 for the motor itself alone. Good ol quality LG products........And they advertise "life is good", tell me is it good having a fridge that's got problems after 2 years? Here's your parts diagram. Good luck
parts for LG LDC22720ST / ASTCLGG - AppliancePartsPros.com