I am thinking brackets...
Seen this before, make sure ALL the bolt are in.
There should be 4 bolts holding the pump bracket to the engine under the t belt cover, than 3 bolts holding the pump, than 1 bolt from the alternator bracket tot he pump bracket, than 2 bolts for the 90 degree angle bracket to brace the pump bracket, and 2 more on the same bracket that go into the engine to hold it true, than finally 1 last bolt that goes through that same bracket with a large cone nut that braces the back of the pump.
So there are 13 bolts you need to check, check them all.