Hi guys first post here, awesome community!

Here is my problem, 3 months ago I bought my dream truck (a land rover discovery 2004) with about 112 000 miles on it and runs perfectly fine. Since I bought it, my rover and I started playing a little game, he makes a new noise and I try to fix it, so far I was able to fix a few things but for this one I might need your help. I know there is a lot of info about knocking engine but I have not found any similar to mine. Here are the clues that I have:
-Knocking starts when hot
-Knocking frequency rise and suddenly stops at above 1200 RPMs
-Noise is coming from under (transmission/ transfer case area)
-Fades and stops when I put the truck in park
-I have a ultra gauge and temps never went above 212F since I’ve had it, it runs at around 204F most of the time.
-Only errors codes I get is from bad O2 sensors (all 4 will get changed in a week)
-Transfer case oil was overfilled by previous owner or transmission oil is leaking in my transfer case (had 4L in it instead of 2,1L) oil was changed 2 days ago and noise is still there
-Transmission fluid looks good and the level is spot on (I did not change it yet)
-All modes work great (4H, 4L, diff lock H and diff lock L)

I have read about the flex plate breaking and making similar noise, for now that’s what I am thinking but I do not feel rough shifthing (maybe comes from my lack of experience with discos). Also a bad bearing between the t-case and tranny would explain the noise and the overfilled t-case but again not certain since the transmission fluid is not low, thanks for any help!

Here's what it sounds like from under

You Tube

 

I would use the stick to ear method and try to isolate it. Then -

Get the Extinct thermostat mod to control and bring down engine temps.
Get a Ultragauge or similar to monitor engine temps in real time.
Get a oil pressure gauge to watch oil pressure.

If readings with the above all fall into normal just drive it. People drive these truck for thousands of miles with ticks and knocks and zero problems. I'm doing it now.

 

Also try switching to Rotella 15-40 oil as well as the PCV mod

 

Don't forget to look into exhaust and vacuum leaks...

 

I have exactly the same symptom and did all the recommended mods as well as fixed small exhaust and intake leaks, but no change. It disappears after an oil change, but comes back after 500 to 1000 miles.

 

Ok, let's look at the clues:

-Knocking starts when hot

• Could be oil pressure, could be cylinder tick

-Knocking frequency rise and suddenly stops at above 1200 RPMs

• Same as above

-Noise is coming from under (transmission/ transfer case area)

• Same as above - frequently engine ticks are reported from this area.

-Fades and stops when I put the truck in park

• So no ticking at all, idling, hot, in park? if so I am leaning toward oil pressure. Disco idles slightly lower in gear vs park.

Start with an inline mod with 180 thermostat. Get the ultragauge and monitor the exact temperature it starts to tick at. If it repeatedly starts at the same temperature (starts at 180, consistently, ticks as long as it is above that temp) then it is likely a slipped liner. Oil pressure takes a bit more because the oil pressure drops a lot between the engine reaching 180 and the oil reaching 180. The oil heats up a lot slower. You can also check the oil pressure to verify.

 

Do you run 15W40?

 

I just looked into it more carefuly and a few things have became more clear:

I still have ticking in park but is less noticable (I have to get close to it)

Ticking becomes noticable about 1 min after starting the vehicle (cold) but gets louder when operating temperatures are reached

I will definetly run a oil pressure test

 

No the previous owner just did a oil change with 10w-30 before I bought it, I plan on switching for 15W-40 in less than a thousand miles

 

As stated above, you could probably drive it forever, if it does not drive you nuts. Mine got worse over time, all the mods helped to some degree. The inline thermostat is invaluable and everyone should do it. I spent years tracking it down, ultimately it was the sleeves, which for the longest time I believed was an urban legend.

I ultimately had a guy pin the cylinders, I got lucky that he was close enough to me, Did good work, fair price, I would go back if I needed to.

Where are you located?