Ok, so I have been searching on here for a few hours and can't really find anyone with quite the same problem I have. So, I drove from San Diego to Missouri to go home on leave, and before leaving never noticed this sound ever. Once I arrived in MO and started driving around for a week or so I started noticing this god awful noise coming from the engine. At, first It really sounded like a bearing or something of that nature was going bad. The noise only happens when I'm just cruising anywhere between 40mph and above. Definitely rattling, but when I was in the process of slowing down it really sounded like something was catching almost like a gear or something grinding in and out. The rattling noise at cruising speeds goes away with a little acceleration, but then comes right back when its not getting fuel. I'm guessing these noises I heard are related in some way. Any help would be greatly appreciated. Thanx in advance.

 

I think that the first place I would look is the idler barning by taking off the belt and check for excessive play.