96 V8 has top end noise

[bmxking5]

Okay, my 96 5.0 Explorer has about 160k miles on it and I've had a noise coming from what I had originally thought was the bottom end for about 6 months. I've run 10w-30 mobil one high mileage in it since I bought it 25k miles ago but just yesterday I used regular castrol 10w-30 and the noise seems louder. The problem had sounded like it was coming from underneath the motor before but I listened today and it's definitely louder from front. Since the beginning, the only way to describe the noise is that a bolt is just rattling around in my engine!

The noise only lasts about 3-4 minutes till it's warmed up then you can no longer here it. The truck runs perfectly when you get on it getting on the highway, etc and has no weird symptoms. The only problem the motor has that I know of other than this is an exhaust leak from the passenger side (not too bad, it goes away when warm also) which I don't believe is related. I tried searching the forum and found something about the lifters, but I don't know if that's it or not. Is there any kind of adjustments that can be made if I took off the valve cover?

I just got a set of Torque Monster headers which will be here later this week and I'd hate to spend all the trouble of putting them on if the motor is about to go out..... Any ideas, please help!! Thanks......

EDIT: Sorry, been listening to it again and its not top end its more of front/bottom end. Still can't figure out where it's coming from...Need to get my stethoscope from the shop tomorrow and listen. Definitely sounds like something rattling around.

 

[bmxking5]

Anyone have ideas? It sounds like it's coming from timing chain/front crankshaft bearing area. If it was the crank bearings it would probably be knocking though right?