Squeaking noise

When I started my 96 Explorer (4.0) this morning, the engine was making a very loud squeaking noise. It seemed to be coming from the rear of the engine (near the cabin firewall). The noise didn't sound like it was coming from the belt or pulleys at the front of the engine.

The noise was loud and didn't change w/ engine RPM's. It became more and more intermitent as the engine warmed. Any ideas what this could be?

Thanks,
Grant

Grant, I was searching for answer for the same problem that you are having with your ford..I have a 1999 ford explorer with the 4.0 pushrod engine and for the last 2 months I have noticed a clicking noise in the engine and was not worried because it sounded like a lifter but 3 days ago it turned into the noise you describe in your post. I am a retired diesel mechanic but have worked on many cars and trucks. I thought at first it was making the noise around the belts but I crawled on up and listened at the rear of the engine and I noticed the noise. It almost sounds like a rocker arm that is binding because of lack of lube possibly a clogged oil hole in shaft. I thought I would ask around before I pulled off valve cover. Have you since found the problem??? I would really like to know before I go forward. Thanks deerecrouse