The effect HARLEY9.mp3 is one of 110 sounds in the Transport category. You could describe the content of this category as Transportation, as well as highway, road, cars, trucks, trains, ships, bus, tire, wheel, commute, traffic, trip, cycle, park, garage, city, and drive.
The full collection of 5,000 FX and music clips are organized into 70 separate categories. They are all 8-bit 22kHz mono in .mp3 format, making them easy to use with most programs. This collection is license and royalty-free for non-commercial use, and inexpensive for commerical use. Click here for detailed usage rights.
(If you don't have Shockwave, you can download the Plug-in Here.)