Well If you want too , take it back to the SOB that put it in there . Do a leak down test on it yourself , to check compression .
If the motor is bad , tell him to get you a new one .
My truck does the same thing , sometimes it almost sounds like a diesel motor knocking away . However mine has 200,000 k
miles on a factory built 4.0 HO . Its kind of expected . :dunno: