I have a 1974 350 enigine in my 85 C10. The motor was just rebuilt 900 miles ago. I was coming home and the motor started rapping . I pulled the valve covers and all the rods and and lifters are fine. I dropped the oil pan, there are no metal shavings and the bearings and crank look fine. I also checked the fly wheel and it is ok also. Can somone help me here?

 

Are you sure the noise is coming out of the motor? I had the same problem and its sounds raspy like the lower end and it ended up being the converter. Does this happen when its in park also?