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?