groaning noise and stiff steering wheel. Not the pump

Yes, fluid has been changed and flushed several times. All new clamps on hoses and properly tightened. Have cycled the steering from lock to lock many times and the groaning has significantly reduced over all. It still is very difficult to turn wheel while stopped or moving slow. Every time I pull into the station, parking spot, drive thru, etc., the noise is louder and anyone within earshot of the car turn to see the nice car with the bad sounds. I have noticed the bubbles in the reservoir, seemingly as though they will never go away. I have lubed every conceivable joint and every reachable pulley shaft. There must be a simple solution to this nuisance sound. I have miraculously cured the entire engine of leaks, both liquid and air. Is it possible my fluid reservoir cap is the culprit? Thank you for your assistance.