I have a 2008 Troy Bilt Bronco lawn mower that recently started making a knocking noise when in drive. At first, we could not diagnose where the noise was coming from when driving it up and down the driveway so we jacked it up and went from there. Even on blocks, it's tough to tell where it's coming from but out best guess right now is one of the following pieces, which can be found under Drive System at the below link:

39) Pulley, V-Type

40) Idler Pulley

83) Pulley Assembly Variable Speed

The parts manual can be found here:
Troy Bilt Parts Lookup

Model number = 13AV60KG011Click on the PDF for MANL:PARTS:13XX60X
769-03866
When engaged into forward and full throttle, the knocking noise is not really apparent. It's at its loudest when I press my foot lightly on the pedal to go forwards. Any help would be appreciated. Thank you in advance.