Sound's like an air leak, mine use to behave funny in hot weather, i thought it was the pump, changed that still done the same, took all door panels off, checked all locks, still did the same.
Solved it by taking the pipe(s) off the pump and blowing down either side, (drivers side, passenger side) if all locks pop up, including petrol flap no leak, if only a one pop's up you've got a leak.
If someone sits in the car while your blowing they should here where the leak is.
Worked for me!!
Hope this helps.
