Started today. Goes away when I step on the brake. Sound varies with steering wheel input. Not very loud. Checked power steering fluid. It's up. 19000 kms on it. Hopefully something simple.

 

First, I would check all of my boosted paths... start at the air box, go to the turbo, to the boost lines, to the IC, to the intake...

Look under the knee bolster under the dash, where the steering linkage goes out into the engine compartment, make sure the rubber boot is still there.

After that, I'd check the cruise control and the wiper system. I'm not real familiar with the 11's....

 

I believe both cruise and wipers are electronically driven.


OP

Check out this thread, may be of some help

 

Thanks much for the info guys. I'm gonna book it in.

 

Another area to examine is the Hydro-Boost hose to the brakes. This has been an issue in the past on some trucks. The liner in the hose assembly fails and creeps into the master brake cylinder and will cause this hiss as high pressure oil runs thru the hose. When the brakes are activated the hiss will go away.
Do a search here on this site in the 3rd gen area. You will find photos and information on this issue. Just another suggestion.
Jim W.

 

which is the link Purplezr posted above

https://www.dieseltruckresource.com/...power+steering

 

yes that is the hydro boost line. take to dealer, they are well aware of the issue and is an easy fix

 

Had this happen on my truck...It was as said above, one of the high pressure lines, either power steering or brake booster.

 

Parts are on national back order until 10/22 so the current fix is temporary. If you don't get the temporary fix done it will eventually lead to loss of power steering assist.

 

don't forget loss of brakes since the power steering pump provides pressure to the hydro-boost for brake assist.

 

I have it booked in for next Tuesday. Hauling 12,000 lbs tomorrow...........