96 disco noise

[breal372002]

I am new to land rover and have recently purchased a 96 disco1.
I knew @ purchase it needed some help ( especially with 135k+) so at first , after reading codes and driving I replaced the y cats,spark plugs and wires, cleaned the maf and sensors, replaced power steering hoses, air cleaner.
It now idles great cold or hot but when I drive it , I hear a hissing sound from inside the LR.
( it sounds like it's coming from the lower part of the engine.)
Could this be a manifold gasket or maybe a cracked manifold or who knows what?

 

[joey]

Hissing sound, could just be a normal rover sound... The Fan will make a lot of noise, so with the transmission and transfer case... so not sure what sound you hear that may or may not be normal.

 

[breal372002]

I dont think this sound is normal. I remember my 73 1/2 chevy pickup had the same noise. I replaced the donut gaskets and the sound disappeared.Please let me know what you think about this one, coz I want to fix the simlest things first. Thanks for your help