Knocking noise even when car is turned off

[Moh]

Yesterday my car started making a knocking noise which initially sounded like it was coming from the front passenger side wheel. However this morning I drove the car to work again started knocking after it had warmed up.. I then parked up in the car park turned the car off however the knocking still continued only now it's sounds like it's coming from the rear of the car.

Anyone else experienced this? Does anyone know what it is?
It has been raining cats and dogs last night could this have caused it?