I don't have a Golden, but do have a Cocker, and he was HORRIBLE for barking at 8 months old. God damn, I used to have splitting headaches all day long from it.
Basically - if barking works (or they think it works), they will keep doing it.
Your dog barks for you to look under the sofa. So you eventually give in and look under the sofa. So he thinks "Ok, when I need help under the sofa, barking is the way to communicate it". Haha.
There are a few things you can do to fix it. Different things work for different dogs.
One way is to ignore it completely. No eye contact, no talking, just completely ignore. Some dogs learn that barking isn't effective, so they stop.
Another way is to teach the "quiet" command. There are loads of resources online about how to do this. Basically, you just wait for a split second of quiet, then say "Good, quiet" and reward. You can then start saying "quiet" when your dog barks, and reward when he stops for a split second. Repeat this daily and doggo should understand what "quiet" means.
The other way is to teach "settle". This is what worked for my dog. Ignoring didn't work - he just loves the sound of his own voice. Look up "relaxation protocol" and follow the steps. Once your dog knows what "settle" means, you can start to use it when he's barking. It basically goes one step further than just "quiet", because you're asking him to shift his whole mental/physical state to a more relaxed one (lying down, being quiet, etc.).
The worst thing you can do is to basically talk back at your dog. This was what caused our problem in the first place. Our dog would bark constantly when in his pen, or when we were out of the room, and one of us would be like, "shhhh we'll be there in a minute" "be quiet" "stop barking" "silly dog" "ruff" or whatever. We were giving him attention by doing this, and not actually training him to stop.
I hope that makes sense!