I'm assuming that you mean 45psi? If the pump is running, it's not usually the motor
that's at fault, they either run or they don't. However, the rubber cups that push the water
through the pump get worn and the pump takes longer and longer to build up pressure. You can buy service
kits for your pump and they are easy to fit.
It's not likely to be an accumulator tank problem. If you removed the pressure tank from the system, the pump should still get to pressure and turn itself off.
One more thing; you mention that the pump is loud? Louder than before? If that is the case, it's usually because there is insufficient water
running through it. Are you sure there's no blockage on the inlet side. Do you have a strainer? Is it clear?