I have just replaced the diesel long block in my car from a certified MB service technician.And have only 6000 miles on the motor.But now there is a very loud knocking sound in the front of the block.The motor is still under warranty but would like to know if the valve train might be the cause or possible wrist pin,I do not have a manual and the car will not make it to the place the work was done.I am a fair mechanic on gas engines but not on diesels.could someone please give me some tips on evaluation of this.