Yes its in the back corner but no do cut the battery
box. Just take out the screws that hold the bench in. If you remove the screws that hold in the power panel you can then pull it forward and turn it sideways to go though the hole. I think the bench it held in by 4 screws on the top side and 4 along the floor. This gives you access to the water pump and back of the hot water tank. As for the noise, if if a thumping noise then that is pretty normal. Some people have has success with adding rubber hoses to the pump to absorb the pulses from the pump, others have added a small accumulator in the system.