i went to to look at a 91 XJ(laredo with 4.0HO) with 160k on the motor. when i got there and the owner started it there was a immediate loud knock that seemed to come from under the intake. the sound stopped after about 3-4 seconds and it knocked once more when he revved the motor a little. he said it knocks like that when it is really cold and when it starts but after that it quiets down and no knock. i took it for a test drive and no more knocks from the motor?? would it be worth buying and what do you think it could be?(i have a jeep but its a wrangler so i know nothing about XJs) i did search and i could not find anything that seemed like the knock that was happening with this XJ. any help would be appreciated