Many times this noise is caused by air in the system. Adding fluid is not enough. You need to run the vehicle and have someone turn the wheel from side to side. This will force the air to bubble out through the reservoir. You may need to add more fluid after doing this. Do not add above the full line.
If you had to add fluid, this means there is a leak somewhere and you should get this checked.
〉 Answered on Mar 8th, 2008 by Lori Johnson, Owner and Instructor at Ladies Start Your Engines
Be careful not to overfill the power steering fluid - it is a pressurized system. It could possibly be a belt or pulley problem you're hearing. To make sure, I would recommend taking the vehicle in to your technician so they can hear the noise and know for sure what is causing it.
〉 Answered on Mar 8th, 2008 by Suzanne Grego, Technician at City of Philadelphia Fleet Management