"knocking noise from the compressor

Good news is the compressor can be replaced, bad news is its expensive. the knocking noise is the compressor and will likely get louder over time. Or may be like that for 5 years.

This could simply be the freon line hitting the compressor or the compressor could be about to go out. I would pass on this unit, if I were you. I would also make sure that you buy from someone that you can count on to provide at least a 60 day warranty and that you can trust to stand behind that warranty (like a local company) rather than buy from an individual. Especially as expensive as a fridge full of food costs. Hope this answers your questions and gives you some peace of mind. :>). Ella

If the noise is actually from the compressor then the spring inside is broke and the entire compressor needs replacement. Usually a $500.00 job.