Hydroboost unit noisy at highway speeds

[Lil Red]

Just got the truck back running mid August. On the dragstrip and on the highway, any speed over ~ 120 kph (75 mph) and up causes the hydroboost unit to growl (same growl as when the ABS system activates in slippery conditions) continuosly. If I slow down to ~ 110 kph (70 mph) the noise will go away. I have flushed the power steering and hydroboost system with fresh power steering fluid but didn't help. I still have steering and brakes. In fact whoaed it down from a 128 mph pass on the dragstrip this past Friday with no issue. Once in a while it seems to have very hard steering when stopped and trying to turn the wheels but I attributed that to the large tires (305-45R-22's). Bad power steering pump or hydroboost unit?

 

[Lil Red]

Found the problem!

As it turns out, it was neither the pump or the hydroboost unit, but rather the 3" DS IC pipe coming up against the hydroboost unit in boosted conditions. Sounds just like the growl you hear when the ABS system is doing it's thing on slippery roads, only continuosly when at higher turbo boost pressures. Need to do a liitle re-routing of the IC pipe