If the oil level is fine and the oil light is on you have no oil pressure and running the engine will blow it up.
It could be a bad oil pump, clogged oil pick up tube, bad bearings.
I have no idea of your trucks history, so a DIY oil change would be a good place to start.
If the noise continues then you need to decide what you want to do after that.

 

Ok thanks. Was wondering if it could be anything even more serious... But I suppose if the oil light is on then this explains the noise I'm hearing.

 

The oil light being on means there is no oil circulating through the engine and the noise you hear is the metal to metal wearing of the parts that are not being lubricated.

 

Right! And if there oil light was NOT on might it be something else other than oil circulation. So I'm going to start with an oil change and rinse. Do you think doing an oil change with conventional and topping off the final 2 quarts with diesel fuel as a rinse a couple of times until the oil drains clean is a good idea?

Then leave synthetic for final change which is what I've been running.

 

No, dont bother, just change the oil, be sure to fill the filter full with fresh oil before you put it on.
Right now you just want to see if it is a oil type/viscosity/oil filter problem.
After that if the noise goes away then look into possibly doing a engine flush.
And for this oil change just use cheap oil and filter, because is the problem is still there you will have wasted all of that money on a oil change.
If the problem then goes away you can change it again in 500 miles with a good oil and filter.
Right now, because as far as we know the engine is toast, go as cheap as possible.

 

In changing the oil I'm wondering if I should drop the oil pan and check the pickup for a clog. How difficult would it be to do this?

 

Sure. wouldn't be hard at all. You might have to jack the front up and support by the frame to get the front axle to drop enough to remove it.

Get one of these:
Gasket - Oil Pickup | Land Rover Engine Parts at RoverParts.com

And one of these:
Gasket - Oil Pan | Land Rover Engine Parts at RoverParts.com

Though instead of, or in addition to the cork gasket, some use:
http://www.permatex.com/products/aut...sket_Maker.htm

 

Thanks! On the DIY charts what would you rate it scale of 1-10? And how long would it take?

 

I would rate that job as a 5, its not hard just lots of nuts and bolts.
Total time 3-4 hours I think, I have not done it but including jacking up the truck, undoing the 24 nuts that hold the oil pan on, cleaning up the mating surface, cleaning the oil pick up and then putting it all back together...

 

A 5 - 6, a long afternoon. Lots of bolts. As alternatives, consider a bottle brush shoved in through the drain opening, using a camera to look at it, see Wireless Inspection Camera - Great Deals on Wireless Inspection Cameras at Harbor Freight, or removal of oil cooler line and back flush with a little solvent - see attached drawing from RAVE.