I have a 1994 f350, 7.5L, E4OD, 4x4 and it has a seemingly random and sporadic low pitched, pretty quiet grinding noise coming from the engine bay or front end somewhere. It doesnt always happen and I can't seem to notice much of a pattern for when it shows up except I do often notice it when the trucks climbing a hill. I figured it had something to do with the driveline because it comes and goes kind of like a bad bearing or something out of balance but I sometimes hear it while stationery with the engine idling. It even sounds like a driveline sort of sound, doesn't sound scary like gears grinding but more like a shaft spinning on a gritty surface for a second or two at a time. The truck definitely has an exhaust leak on the rear passenger area of the exhaust manifold like 7.5's like to develop. Is it possible an exhaust leak could make a sound that sounds like a low quiet grind? What else could be causing this sporadic sound? I'm leaning towards something in the engine as its got over 200k miles.

 

"Even when stationary I hear it" I had a bad smog pump that sounded similar and it is a somewhat common problem. Get a long screwdriver or a piece of hose and from the passenger side or front locate the pump at the bottom and listen to it especially when stopped. You will know if it is the issue. Always use caution when working on a running engine and park in a safe place.

 

These are the kind of ideas I knew people on here would have. I never even considered the smog pump but I could imagine it making the noise I’m hearing. Thank you, I’ll check it out.

 

Exhaust pipe warping and touching the body when it gets hot. Replacing the engine mounts and body mounts will fix that problem.

 

Since the belt has to come off to check the pump start it up and listen if the noise is coming from a different location. Also a good time for belt replacement ,check all the idlers , alternator, water pump and compressor bearings.

 

Remove the serp belt and twist all the pulleys around
Possibly run it with the belt off for a moment
Power brake it to check if the exhaust is hitting anything
Tip in moan from the trans? if real slight