Partner of mine has an Exmark 27(Kohler)/52 that is making a slight knocking noise at idle. Think we identified the area it is coming from. Hydro pulley area is the location, but can't figure it out from there. I believe it's coming from the pulley with the spring on it. Is there anything we can do to fix this ourselves through trial and error before we take it to the shop. I'll include pics of the area. Any help will be greatly appreciated.