2000 Ford F 150 with only 68k miles. Never had any issues. We had a water pump problem which caused us to have to have the heads replaced. We get the truck back and now it has an intermittent knocking coming from the top of the motor. We asked the guy to come back and look at it and he doesn't know what it is and is suggesting that we replace the motor. We used this guy cause he was recommended and the price was right. We just want the truck fixed and don't know where to start. Any suggestions would be nice.