2004 Discovery 140k miles was running great. Oil light came on. Now there's noise coming from engine, doesn't sound like a rod kock but something's wrong. Where do I start?

 

Probably oil pressure not a low level

 

do not drive it until you have the oil pressure tested.
the purpose of the light is not to tell you it is low on oil, it is to tell you that there is no oil pressure

 

Oil pump broke

 

Check oil pressure first, Might be as much as a by-pass valve in filter failure or failed sending unit. Oil pressure test will tell you if pressure is up to par, if not, yes I would agree with pump. But also if bearings are wore enough, this can lead to low pressure, an oil leak down test will be needed after oil pressure test. Not a Rover Tech but 15 years experience on Rover and 49 yrs Jag.

 

oil pump failure x 2 ... front cover will have to be removed to verify.

 

Ditto. You probably have an outer gerotor on your oil pump with one or more cracks...causing low oil pressure. Take off the timing cover to expose the oil pump; examine your main and rod bearings while you have the oil pan off. Chances are you've got fried bearings, too. Inspect timing chain and sprockets. At 140k miles, it's a good time to replace these.

Does the engine make a tick-tick-tick at low idle?

 

X1 or faulty pressure switch. Whatever, don't start or use the truck until it is established what is wrong otherwise you'll 'lunch' the engine if it's the pump broken.

 

Mystery solved....oil pump came apart and took out a big chuck of the timing chain cover. No large debris in the oil when I pulled the pan. However after I drained the oil out of the pan you could see very tiny sparkles of gold ie: brass or copper.

 

Ugh. Better do you main and rod bearing while its down.