2002 Saturn Sc1 Hear Sort Knocking Sound Drive Oil Fluids Fine Sounds

I hear a sort of knocking sound when I drive. My oil and fluids are fine, and it sounds like it is in the axle...definitely not the engine. The sounds speeds up or slows down in correlation to my speed..it seems like the sound is in the spinning of the front axle. There is no sound in idle, and no abnormal idle. When I am on the breaks, the sound does away. The car runs fine, I just don't want to make the problem bigger. I noticed it the first time I drove after a week of it sitting when I was on vacation.