Power Steering Pump

[72ratnova]

so my power steering pump on my 72 nova was making the noise like it was out of fluid, but was good on fluid, so i figured the pump just went bad, so i replaced the pump and the press. and return lines. once back together, no problems, drove the car for 5 days and tonight it started to make the grinding noise, check the fluid and was just fine? so my question is why would it work perfect all week and start acting up now and any idea's on whats gone wrong