I disassembled the valve today to make sure everything inside looked good. No problems. Tightened the set screw down to the recommended 3 turns and I'm still getting the knocking noise at idle when the power steering pump or AC put load on the engine . Took a look inside and noticed when the vacuum pulsations begin under load, the valve vibrates open/closed causing the knock. This pic was taken at idle.
The only way to prevent the knocking is to either tighten the set screw really far, or loosen it to the point where it is not making contact with the plate. I already had the manifold off last weekend and ran a new vacuum line to ensure there were no kinks and redid the T connection so there would be no sharp angles. I'm out of ideas at this point... What could be causing pulsations in vacuum pressure at idle?