analog stick very sensitive randomly while using d-pad

Randomly the analogue stick will move slightly in a direction while I am using the d-pad. It works excellent otherwise.

QUICK HISTORY:

-The analogue is used from another PSP1000 since my old analogue died.

-The exterior left side of the case was creaking and I noticed a slight separation. It appears someone tried to pry it with a tool of some kind. I put a small piece of cardboard inlay and it's completely unnoticeable and stopped the creaking, sealing the case back into place without allowing it to move. I highly doubt it's putting strain on the analogue but I wouldn't exclude this fact.