I've' been hearing Noise and feeling roughness when parking in my wife's '03 Caravan 120,000 miles. No leaks and fluid is full. Notice noise is louder after 30 minutes of driving. It Sounds like low fluid Groan. Although I see no Pump or Rack leaks should I be thinking of a New Rack Assy. ? Any additives help this ? Seafoam ? Thanks and Happy Holidays !