2000 Landrover Discovery II 4.0
91k miles

engine is making that notorious knocking noise under the vehicle. Knocks when engine is cold or warm. I crawled under the vehicle and it really seems to be coming from the cat. When I tap on cat with hammer, I can't here any rattle or corrosion. My question is, in the cases where the knocking comes from the cat and sounds like a knock, will the knock increase with rpm's? I can only here it with windows down or I'm outside the vehicle, if that tells you the volume of the knock. thanks for any info.

 

hi, ive never herd of a knock from a cat ? usually a rattle or meow from them, my guess is that theres a knock in the engine but the cat / exhaust system is just amplifieing the sound ?
my rule is if its quiet in the car dont worry about it ! but im used to driving older stuff with funny sounds HaHa good luck hope this helps.

 

Camp

have a look at the heat shield of the catalytic converter. Sometimes, the welding gives out
and it rattles as a result. Will post pics in Discovery forum.

EVN137

 

Turn your engine off, then hit the cat, if it rattles, it is shout and in need of replacement.
If it sn't the problem it could be a broken flex plate or low end bearing issue.