Groaning noises are usually associated with low levels of power steering fluid. Are you getting this noise while you're driving and turning, or while you're parked and turning the wheel side to side? If you're parked and doing it, then I don't see how a control arm bushing could have that affect? I would think if anything outside of your pump making that noise could be your outter tie rod ends going bad, but I don't think they would groan, but rather pop. Bushings don't really "groan" as if they're straining, they just pop/bang/crunch/squeek. The guy who installed the rack, is he a Lexus mechanic? I ask because i've heard of specific hoses needing to be used. I've also heard of some kind of pressure valve incorrectly being installed. Honestly, to me, it sounds like your pump groaning to strain.
Another thing that could be causing the pump to strain, and probably a likely candidate, is the solenoid in the rack!! It's got that tiny screen in it, and when it get's clogged up, your steering gets heavy. The solenoid opens and closes depending on your speed. The lower the speed, the more open it goes, which allows the pump to assist you more in turning the wheel. If it's clogged up, your pump might not be getting enough fluid in it to be effective, which would cause it to strain, and in the long run, would burn it out. If your new rack is a remanufactored one, then it is QUITE possible the solenoid was never cleaned.
If you do a search for the power steering solenoid, you'll see the threads, and some pictures as well.
Edit: Here ya' go Bama'!
http://us.lexusownersclub.com/forums/index...enoid&st=45
I agree with NC211. There may be a lot of air in the system. Get the front wheels off the ground, loosen the PS filler cap, turn the key on (but don't start) and go "lock to lock' with the steering wheel about 4 - 5 times. If it is not better....then go after the solenoid..