"Oljud" and "oväsen" are mostly interchangeable, but I'd say that the differences are that "oljud" are mostly noises coming from ONE source while "oväsen" is usually noises from several sources at once. "Buller" on the other hand is most often noise coming from mechanical things, like cars, machines and so on. Examples: Pianist riskerar fängelse för ”oljud” - Pianist risks prison for making noise. (one source here... The piano.) Semestern förstörd av oväsen - Vacation destroyed because of noises. (one or more noise sources) Buller från trafik och järnväg - Noise from traffic and railroad. (The noise comes from something mechanical)