Engine problems of the 1998 Acura SLX

In June of 2003, we took our 1998 Acura Slx w/45k miles on it into stevens creek isuzu dealership for a major service and to check out the "pinging/grinding" noise that we had been hearing for a long time. We were told they couldn't duplicate the noise. In June 2004, we took it to the reno isuzu for an oil change and to check out the noise and we were told that we needed a new engine. Our car now has 54k miles on it. We took it to an independent mechanic shop for a second opinion and were told that a rod was blown and a new engine would be needed. The car is still in the shop. We paid $4k for a new engine so far and will owe about $3k in labor & misc. Parts. We feel that since this problem started while still under "mileage" warranty but could not be diagnosed, Acura/isuzu should pay for the engine and labor that we have incured. Our mileage is extremely low and there should be no reason to replace the engine this soon. We own a 1993 Jeep cherokee that have 117k miles on the original engine! we have read many complaints on other websites about the Acura/isuzu engines blowing so early. We are very disappointed and will never recommend nor buy an Acura/isuzu again.