Street musicians are usually pleasant surprises while walking along the side of the street. You're just as likely to hear the Eagles' "Hotel California" as you are a Thai number in the city, but many times I hear something new - and I like that.
There's also a variety of sidewalk entertainment that's less pleasant: the mobile singers. Sometimes sitting in one spot, sometimes being accompanied by someone holding their small but powerful amplifier they sing Thai songs. That in and of itself would be fine, but it's often at a decibel level higher than the traffic noise, and a good ten times as shrill.
Unlike the khim player or the hotel singer who played "Imagine" for me, many of these singers seem to be blind. I'd say a good third of the musicians I've seen on the sidewalks on streets or in BTS areas appear to be blind. Just my own casual observations with nothing to back that up, though. Both of today's players were blind.
The guitarist at the top was sitting along an elevated walkway attached to the Victory Monument BTS station one morning, and played rather well. The man playing the flute below was just along the street, and although he used an amp it wasn't set to a painful level.