What's that rattle?

Hi-
Any and all consideration, thoughts, theories, info is appreciated. Please listen to the video clip and let me know if you have an ideas.

I started to hear a slight tap Friday afternoon. The sound seems to be coming from the top driver's side of the block but hard to pinpoint. After a local mechanic took the belt off, tried to see if any pulleys were loose, I turned the engine on and the tap was still there I had it towed to a pro that very afternoon. The current thought is that it is in the valve train. I theorized push rods and/or lifters.

Against my own (and the pro's) better judgement I picked it up today, drove it 10 miles to car quest, poured 10 oz of seafoam! into oil, and 1 bottle of Lucas into fuel after toping off a half tank with 91 ethanol free. Needless to say my fingers were triple crossed. I figure if I need to tear it open to figure out what it is, there's not too far to go before the cost of replacing makes more sense anyway so if I can take the chance I will.

Drove it to the highway. Drove 20 more miles home. At about 65 the noise settled too low to hear. I thought it was gone and I had normal cruising power and a smooth ride. Inclines were not a problem. Tapping turned into an inconsistant rattle can when I slowed to exit the highway. Was still considerably lower in volume than in the video. It was also inconsistant when driving. Speed lessened the rattle, while slowing and coasting brought it back. Felt like approaching 50 mph was its cure. At slow speeds, power is a problem and the rattle turns into what you would expect a wide open rock crawler without pipes to sound like.

No lights on dash. Noise is loud when hot and quiet when cool.

Thanks,

Almost Cooked

http://youtu.be/BAq-sYHPL3g

____________________
04 Disco II

The lightness of the tapping is indicative of tappers/camshaft/followers.
I'd say you have a top end rebuild in your future.
I do think you should get a read on actual oil pressure from idle up before investing money. If there is a pressure problem what we're hearing is the tip of the iceberg damage wise.

Thanks. I'll continue to update as I go.

Update #1: turned my truck around in the driveway this morning and this was the result. Causes?
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Update 2:
After a look at the Rave Manual this afternoon and realized that it was the PAS pump pulley. Which makes sense because the guys I bought it from said they put a new one in. They were less than stellar.

Got home from work and turned it over. Sounds normal. A new pump and pulley in my future.

It's times like these that makes me believe AAA is the best decision I've since buying a Rover.