Cadillac Repair: 1983 fleetwood pulley driven vacuum pump, shaft bearing, vacuum lines

Question
I have a 1983 Fleetwood brougham. I changed my valve cover gaskets. I got everything back together and fired her up there was a loud knocking noise like a woodpecker. I narrowed it done to the vacuum pump by taking the belt off, but could not figure out why it started making this noise. To be clear this is the pulley-driven vacuum pump near the front of the engine on the drivers side. I pulled it off and took it apart and couldn't see anything out of order. Shaft bearing seemed OK, cam lobe housing was filled with oil, diaphragm button felt good. Bought another pump and pulley at the junkyard, tried it, same noise. When you pull off the outlet hose of the pump the noise softens a little until the hose is reattached. I would appreciate any help. thank you

Answer
Are you POSITIVE that you reattached all the small vacuum lines to the big black plastic switching valve near the other side of the engine as there are small vacuum lines attached to it.

did you try spraying the belt with some silicone just to see if the noise changes ?.