Here is a service bulletin regarding the power steering pump.
Power Steering Whine Noise - keywords fluid gear hose idle pump turn - (Mar 4, 2008)
Subject: Power Steering Whine Noise
Models: 2003-2006 Cadillac Escalade, ESV, EXT
2003-2006 Chevrolet Avalanche, Suburban, Tahoe
2003-2007 Chevrolet Silverado Classic
2003-2007 GMC Sierra Classic
2003-2006 GMC Yukon, Yukon Denali, Yukon XL, Yukon XL Denali
2003-2007 Hummer H2
This PI was superseded to update models and Recommendation/Instructions. Please discard PIT4208A.
The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
Some owners may comment of a power steering pump whine noise. After normal diagnostics you may find the noise to be coming from the power steering pump. This whine noise is most commonly heard between idle and 2000 rpm coming from the power steering pump.
GM Engineering has not evaluated this product, but reports from GM Dealers of flushing and refilling the power steering system with Valvoline SynPower Power Steering Fluid have reduced or eliminated this noise. Valvoline SynPower Power Steering Fluid is a synthetic fluid and is available at most auto parts stores in quart size containers. In most case 3 or 4 quarts will be needed to flush and fill the system.
If Valvoline SynPower Power Steering Fluid is not readily available, replace the power steering pump ordered from GMSPO only. Power steering pump improvements have been made which will help eliminate this noise and are currently available from GMSPO. Use the parts catalog to look up the correct part number for your application.
Monday, June 7th, 2010 AT 11:39 PM