If you double isolate the pump you won't hear it - whether the engine is running or not.
If you mount the pump solid then you will hear it.
Double isolation uses a rubber isolator on the back of the mounting panel, one on the front of the mounting panel, and another over the top of the pump bracket. There should be a tube that runs through the middle isolatorand pump mounting flange. The screws go through the tube and all the isolators to keep the screws from transferring noise to the panel.
This way the pump floats between one pair of isolators and the whole rig floats on the mounting panel beteen isolators, with the screws floating in the tubes. No noise transferred to the panel and any noise in the pump is deadened by the isolators.