A survey is made of compression brake noise levels in heavy duty diesel trucks, using test procedures based on the ISO and EPA driveby acceleration noise tests. The data shows that compression brake noise levels are very high if worn out or open stack exhaust systems are used. Compression brake noise is also audible with OEM exhaust systems and, in at least one case, potentially objectionable. Two methods for reducing brake noise are investigated: improved mufflers and the use of an exhaust brake with the compression brake. Both techniques demonstrate a potential for reducing compression brake noise.