Ok, not really sure what's going on so didn't know where to post this. If I need to post it somewhere else, please let me know. I just bought a 2004 Ford Explorer 4WD. Didn't notice the sound when I purchased but now I do. I want to say it sounds like a loud bee buzzing noise when I accelerate. It also does it when I first start it up for the day. Oddly enough, it doesn't do it when I am in reverse. Any help will be appreciated. Thanks.