I had the same exact problem a year ago. Nobody had any ideas at all, I knew it was coming from the front end so I started replacing components. It eventually stopped after I replaced the idler arm. I had noticied that it would start to make the noise after going over a bump and that is I hit another bump it would go away. It doesnt make a whole lot of sense as to why it woudl be caused by the idler arm but that is what made the noise stop for me.