A Harley-Davidson motorcycle is not as loud as a Concorde. The Concorde was a supersonic passenger aircraft known for its extremely loud engine noise during takeoff and landing. It produced a distinctive and powerful roar due to its engines' design and the high speeds at which it operated.
On the other hand, while Harley-Davidson motorcycles are known for their unique and iconic sound, they are not comparable to the noise produced by a Concorde. Harley-Davidson motorcycles generate an audible rumble and deep exhaust note, primarily due to the design of their V-twin engines and the exhaust system. The sound can vary depending on the specific model, aftermarket modifications, and the rider's preference, but it is not on the same level of loudness as a Concorde's engines.