Q: Engine began knocking after oil ran low

Unfortunately, hearing an engine knock is not a good thing. Hopefully, you were able to shut the car engine off as soon as you heard the knock. It may be a long shot but one tip you can try first is performing an oil and filter change on your XJ8. Once this is done, start it up again and notice if the knock is still there. If the knock is still present, then it is likely that internal engine damage has already occurred. Enlisting the help of a certified mechanic will help eliminate the guessing and give you an accurate diagnosis the noise on your Jaguar.