I agree it sounds like he has issues with loud noises and, if it's not just a hearing issue, that he needs to be desensitized to them. Here's a good video on barking at noisy things (hah second one of her video's I've linked today that are ever-so-appropriate =P): YouTube - Dog Training- How to train your dog not to bark- Episode 1
Up until a few days ago Willow was a barking nightmare from the depths of all puppies terrible. Annoying was a light way to put it. Her problem wasn't just loud noises though it was loud noises and everything in-between. She's now a good puppy 95% of the time. Unlike a lot of people here, I'm the furthest thing from an expert on training dogs or on behavioral issues -- if anything I'm ultra-novice and do some really stupid stuff when it comes to training Willow – I’m one of those people that lurks around here for the pro advice from people like Criosphynx and Dogshrink. One thing I did for desensitizing for distractions may be helpful. =( I don't have a link or video to anyone's ideas on it though since I made up the game by a hybrid of a few different methods written and video taped by a few different people. It's pretty much similar to what Fawkese wrote.
At first I started off with things really simple. I made it rain chicken for her. I waited until she was nice and relaxed and I started dropping very tiny (tic-tac sized if not smaller) pieces of chicken (or cheese) between her toes every 2 or 3 seconds. Doing that sure woke her up. After a minute or so of that I extended the time to every 6 to 8 seconds. She started to get frustrated wanting the chicken earlier and she started barking. At that second the chicken rain stopped. When she was quiet again, it started raining chicken again. As long as she stayed quiet, it continued to rain chicken. Any time she'd bark, the rain stopped. I had taught her speak and quiet and the first time we played this every time she'd bark I'd say "quiet", the other times we've played it though I haven't used cues since I found it works better when I leave it to her to conceptualize how it works.
So, I kept swapping the durations on the chicken dropping and after a bit she caught on that sometimes the chicken falls faster, sometimes it falls slower, but barking makes it so it doesn't fall at all. Towards the end of it I got up to around 45-seconds. Once she understood the basics of the game I turned it up a bit.
My boyfriend was playing music and so I started dancing about the living room moving at different paces and in different positions that Willow was very unfamiliar with. I moved into and towards her so that she was encouraged to move with me. As long as she stayed quiet, chicken continued to drop, if she barked the chicken stopped falling from the sky.
After a bit she stopped caring whether I was dancing, moving towards her, moving around her, or even leap frogging over her; which I did. She was excited, happy and her tail was wagging but she just kept her little barking motor off. Once I was leap frogging over her, which I figured had to be extremely distracting, I decided I needed to turn up the heat a bit more. She likes our couch a lot but she can't get herself onto it. I went and stood on the couch and danced away there, and then I stood on our heavy wooden coffee table and danced away there. This put her in very unfamiliar circumstances and she barked at the abnormality of it all. But she eventually caught on that barking means no chicken and she stopped that too.
At that point I started introducing sounds into the mix. Strange sounds I don't normally make but that I knew would get her attention fast and antagonize her a bit. It worked well until she caught on and then poof no more barking at those.
I kept going like this turning up the distraction level bit by bit. The final stopping point was when I was calling her name over and over "Willow, hey it's Willow, got-ya Willow, Willow, Willow, haha, Willow it's you, hey Willow," in a high-pitched extremely excited tone while leaning over her and tickling her tail. At that point she started barking away and wasn't going to quit (but really if I were her I wouldn't have either...) I stopped the distractions then and told her "quiet" and with the stressors gone she simmered right down. I waited a few seconds and gave her a massive amount of chicken. She was mentally exhausted from it all and was nice and calm after that.
We've played the same game a few times since and the heat has gone up to where I've literally rearranged the furniture before she'll bark.
Willow barked at everything I could think of and it took a lot more than doing that game to get her to stop but I think (or at least hope) that game helped her conceptualize what is and is not rewarded. Once I figured out how to communicate my problem to her though, and express how in bark-free and calm states really good things happen, then eliminating the annoying barking was a quick process.
Your pup sounds like its only barking at loud noises. Perhaps doing something similar but creating the noise yourself to where you can control it would work. Like use something he's not already afraid of (like don't use the vacuum cleaner) that's a distracting sound but isn't scary and annoying to him, and then work up to annoying sounds, and then build it to where you have the vacuum cleaner (or perhaps a blender since it's a similar sound) out turned on and just running in the background so he gets the idea that the background noise without him barking means good things rather than scary things happen.