engine noise when warm
 

1994 disco 1 111000 miles just started making this strange noise only when warm loud tap sounds like its coming from left valve cover checked oil pressure
40-50 cold, 30-40 fully warmed up fairly new to the rover world. Any issues with rocker shafts wearing and causing this noise?

2 things to check first, exhaust manifold bolts and then the cats.
I am betting on the exhaust manifolds being loose or cracked, very common.

As for the cats, tap on them with a small hammer and see if they rattle from the inside.

Also what oil are you using? The wrong oil weight can cause engine noise in these trucks.

hummm I think we own the same Disco

My drvr's side cat makes a knocking/tapping sound. I was sure it was a rod knocking it can be that loud. I tapped it with a hammer while running and the noise intermittently went away.

Noise
 

Tried tapping on both with a mallet no change in noise but it sure sounds like its coming from that area!!

With the engine off tap on the cats, do they rattle?

Im wondering out loud if the tapping noise would follow the engine speed?

If you cant determine that the noise IS coming from the cats or exhaust manifold, remove the lh valve cover( since that's where you feel the noise is) and let the engine run with the cover off, from start up cold to warm, and try to determine which rocker arm(s) is/are making the noise. Mine had the same symptoms and after much ado I found that the steel insert in 2 of the rocker arms(where the push rod ball end fits) was loose at running temp but not loose @ cold start temp....and causing the "tapping / knocking". keep us posted with what you find.

Start off by verifying the tightness of the bolts at the exhaust manifold to the y-pipe flange. The gaskets at that interface do tend to burn thru eventually, so you may need new gaskets. On mine, you could feel the exhaust leak with you hand right there. If you do have to change the gasket, have new studs handy because they do tend to break.

Also what weight oil are you using in it. I put 5w30 in mine one time, just because I had it on hand and wanted to use it up. I found out quickly that it was too light and got a lot of noise. Changed over to 10w40 Castrol extended milage and the noise went away. Rotella 15w40 is also highly recommended.