He sounds like my Tucker. Tucker is nervous, to him a strange sound may mean a strange person is in the yard or house so he barks. My plan is to take inventory of the sorts of things that set him off and then use them in a training session to control his barking. For example is mom is cooking and she bags the spoon on the rim of a pan to bang off excess sauce or something he'll bark his head off and then do gruff growly barks for the next several minutes because he is nervous.
I'll either tell her to bang and click his clicker at the exact moment and start pumping him full of treats or, if that doesn't work, let him bark until he stops, then click and treat. OR I might try the first method and if he barks remove him out into the hallway. I'll likely have mom stat with a single, quiet bang and then work up to a normal several, loud, fast bangs.
Then if I find one method that is successful I might add a cue. Then I'd move on to other noises that set him off. I'd do as many as I could and hope he might generalize or that I'd be able to apply the cue to other sounds. I'm not entirely sure how I'll go about doing it, it'll take a lot of trialing to see what's gonna be effective and practical and what just isn't going to work.
I tried clicking and treating him when someone knocked on and came through the door the other day. Didn't work at all, he didn't bark at the knock, took a treat, but then he started going as soon as he saw someone was coming through the door and he ran at them instead and choked on his treat. Treats, at least those treats, are not as important as freaking out at guests is. I think maybe next time I'll start with him on a leash and MUCH farther from the door, like out of sight of the door and I might see if toys will work better or worse. I also might use the leash to remove him into the bathroom when he barks and wait with him until he's wuiet, then let him back out and continue treating/playing as he's silent, then take him back again if he barks.
So I guess my advice is if there are any things you KNOW he barks at, use them for training and start with a very light version of the stimuli so he can be successful and you can reward him IMMIDIATELY before he has a chance to start barking. Then continue with frequent rewards for silence until he is unlikely to want to bark at the stimuli anymore. If he starts going ballistic remove him from the situation and try again but either improve the timing of your reward, improve the reward (better treat), or make the stimuli even lighter (less loud, less long, less close, etc.).