2000 VW Jetta making a drumming sound from front of car.?

I have a 200 VW Jetta automatic, that makes a drumming sound that comes from the front of the car after I drive it for about 10-15 min. It only does this at speeds over 45 mph and only does it while pushing on the gas. If I let up on the gas the sound stops but will start up again once I accelerate. Any ideas to what this may be?