hey everyone I got a 1990 f150 with a 351 4x4 when I got the truck it had no muffler on it and running everything sounded fine well I put a glasspack on it now sounds like it has a rod knocking if I take the muffler is goes away any ideals thanks.

 

You may have an exhaust leak in the engine bay.

 

I was kinda thinking the same thing thanks for the help i appreciate it.