Blue barks when he's excited, so any time it looks like we might be going out, or if a nice shiny new toy appears, or the pussycat comes into the room, or our neighbour walks past the window, or the courier arrives with a parcel, or the post arrives, etc. etc. etc.
I'm also quite sensitive to noise, so I feel your pain. I wait with much interest to see if you can curb it!