I have an old refrigerator that has started making a noise when it's running. I have replaced the freezer fan and also tested the fridge without the freezer fan running (no difference). I have checked the condenser fan; it's fine. I have checked the compressor and that is fine too (I have listened to it with a stethoscope and it just purrs). The noise seems to come from the back inside of the refrigerator but it is not related to any of the components I have mentioned.
Any ideas? Could it be a partially blocked refrigerant line?
Thanks,
Vic