Does this sounds like a loose liner or stuck lifter/ bad rockers or valves?
 

liner! 95 percent of time i would say its cylinder sleeve

Link won't work for me.

It does now.
Hard to tell from audio, but sounds louder and heavier than typical valve train noise.
Sounds alot like mine, which I'm in the process of removing the engine, as I think I have a slipped liner also, as I've checked and eliminated everything else.

Seems to me its a lifter problem. I dealt with that noise for years and at times much louder. Until I replaced the head gasket and cleaned up the top. It all disappeared no tick for over a year now. I shot a video when I checked another disco for sale with liner problem and sounded much different.
Having 3 discos with high milage, IMHO, ticking is more often than having a loose liner problem. Im not even sure how many people in this forum had loose liner problems, I have seen 1 or 2, and not even documented if it was an actual liner at the end. But stuck lifter? Yes!

Lifters I wouldn't think have that much of a solid "ping" note.

I had a broken rocker arm that sounded exactly like that. Turned out the valve spring wasn't fully seated, caused spring bind and broke the rocker. -My fault; when I re-did my heads I didn't pay enough attention to my work. I would pull the valve cover first and inspect things. A collapsed lifter would probably cause the same sound..

That is EXACTLY the sound I had.

What fixed it?

There's a small hole that feeds the rocker oil. Most of mine were clogged.

Take your valve covers off and check the valve train before you get into the sleeve BS.

That is just a lifter which is bad.

This is because the noise will speed up with the speed of the engine.

If your liner is loose and you speed up the engine the noise will lessen and go away.
That is because the liner can't move up and down as fast as the piston is going up and down in it.

Maybe you can clear it with a few good oil changes or putting in oil cleaner additive for maybe 300 miles and then drain it and put in clean oil.

You could also try thicker oil. But it is winter so that is not a good idea.

possibly check EGR valve which may be caked with carbon deposits.....I'm currently trying a couple things myself on my Disco II; I'll try to let everyone know if I have success.