How old is your Golden? We had one that lived for 12 years, about average. He had a stroke and fat pockets that had cancer, but bark? No, he could be outside on the deck, forgotten for some reason, and the most he would do to attract attention would be jump up and down. He weighted over 80 pounds so the jumping did make some noise.
He could bark, but did it very rarely to the end of his life.
You say you have an old dog and he may be exhibiting these behaviors due old age, like when people get old and some mental deficits start to set in. Also, how is his hearing in general? How is his eyesight? You may want to have that checked out. The lack of appetite may certainly indicate something is going on and it might be a good idea to get an exam and blood panel done. Hard to watch them get old.
This is a behavioral issue. He needs to be trained to bark only when someone knocks on the door. You can do this by practicing with him every day. This will involve two kinds of training: 1) bark only at a doorknock. 2) No barking at other times. These should be done seperately, otherwise you will confuse your dog. Knock on the door at random times, no bark, no treat. Continue this until you feel that he has it down: knock, bark, treat and praise. Do only this part for as long as needed. Once he has learned this, move on to no-knock, bark, squirt of water. 10-15 (adjust this time as need... at first you may only want to ask him for quiet for 5) minutes of quiet, with no-knock, treats and praise. Get him used to the command 'Quiet', and when he obeys, treat and praise. Goldens are highly trainable. If you commit to training, your dog will commit to pleasing you. :-) Blessings to you and your dog - Blu