I purchased my 99 Isuzu new and havn't had any problems with it until about a couple years ago. My engine sounds like a diesel... I brought it to a Isuzu dealership and said that the noise is deep in the engine. What is that supposed to Mean..... The only way that they would know what it is would be to take the engine apart..... $$$$$$
I am putting in so much oil I should buy stock in it... Is this normal should I look for a new engine.... I have 120 k on it now.

Anyone else have a 99 Isuzu diesel!!!!!!!!!!

have you ever ran it low on oil?

that knocking sound is most like the start of a spun bearing. This is a super common problem on +98 Troopers and some Rodeo's.

Also,

have you changed your timing belt yet? if not the knocking could be due to the timing belt tensor. But since you're using a lot of oil it could be the spun bearing.