Land Rover Repair: Engine Tapping in 04 Discovery, land rover discovery, rpms increase

Question
I own a 2004 Land Rover Discovery SE with 64,000 miles.  I purchased the car about two months ago, and the engine just began making a tapping/ticking sound.  The noise is coming from the valve train mostly on the driver's side valve cover area.  My local mechanic has replaced the lifters and push rods, along with the serpentine belt tensioner.  He's also thoroughly inspected the exhaust system and says the oil pressure is 55lbs cold and 15lbs when warm at idle.
I don't know much about the history of the car, but my mechanic says it appears to have been well-maintained.  He says the engine is extremely clean and in good shape.  The noise was constant prior to him replacing the lifters and push rods, but now it seems to start after the engine has warmed up a little.  The best way to describe the noise is that it sounds a lot like a diesel engine.  A loud diesel engine!  The knocking sound seems to correlate with the rpms.  When the rpms increase, the knocking gets faster, and when the rpms decrease, the knocking slows down.  My mechanic is at a loss at what to do next.  Any advice you could give would be greatly appreciated.

Answer
Hi Donny,

you'll have to take it to a LR dealer.  Sounds like you may have a dropped cylinder liner but the only way to tell is to open the engine up and have an expert eye take a closer look.

Best of luck with this repair,

JohnMc

NB:  Happy New Year!!