Autopilot ST5000 Plus w/ Type 1 Pump

My autopilot was installed in 2001 and continues to work properly, except for a pump noise.

The Type 1 rev pump (A12010) started making an unusual noise while pumping to port, but sounds fine while pumping to starboard. I recently bled the system to see if air was the problem, but the noise continues.

I am confused why only the noise in the port direction and would like to repair before its a big problem. Any suggestions will be appreciated.

Thanks, Paul