I have a 2003 Lexus ES300. The car has about 60,500 miles. A few months ago, I got major servicing done on the car. The timing and accessory belts were replaced, new transmission fluid, new water pump, alignment, and tire rotation/balancing. Once I got the car back, I felt that when I accelerated, the engine was louder and not as smooth. The cabin noise had basically increased a bit and the accelerator needed a bit more pressure as there was a bit more of resistance. I assumed that this was due to the new timing belt. I figured that it just had to be worn in a bit or maybe it was too tight. Recently it was noticed that the car made this strange sound on the highway. The more and more I have been driving it the more often it occurs. Now it seems to be consistent when the car is in motion. When I hit the brake and the engine disengages the noise goes away. It also might be since the car is going at a much slower pace because it didn't make this noise when being driven around 10mph and under. However, the noise is consistent when the car is cruising at 30mph and higher. The sound is hard to describe but it basically sounds like something could be loose or like a rattling noise. It is loud enough to notice when listening to the radio/music. Does anyone have an idea of what the problem could be? Is it the timing belt? Any responses would be greatly appreciated. Thanks.