I have a 1994 ford f150 300 inline six, and when u rev it but a bit and let off the gas it has a fluttering sound, has anyone else has this problem?? I have had different mufflers on this truck and it all does the same.

 

Most likely the emissions check valves fluttering.

 

Is this normal?? or does it need to be replaced, cause i never heard anyother trucks that is the same year as mine