the pouring sand sound that you can feel in the steering column is air bubbles in your power steering fluid. I literally JUST dealt with this in my Monte SS, except mine got so bad the pump stopped working. I changed the fluid and it's good now (except I still have a leak somewhere). What fluid did you use when the rack was replaced? And let me guess, the sound is there when you're hands are off the wheel, but as soon as you start initiating a turn, the sound goes away until the wheel is straight with no steering input again, right?
