All the time I've owned my Z, I've had a whooshing sound from the power steering. I've done fluid flushes, done the bleed procedures (found no air) and it's still there.

It's a constant sound when the wheel is getting input, and it's not a whining sound. Just a whooshing/rushing sound. Quite noticeable though.

Would it be some kind of bypass valve or something? I do have 10 inch rims up front, just extra load on the rack and pump?

 

If you're using extremely wide tires up front, the "whooshing" sound is likely from the PS rack as it struggles to give you adequate assist. Be careful, as the loss of that power assist will likely leave you struggling to steer. Check the BCM section of your diagnostic system to find if any PS codes are showing up.

 

Yeah, reasonably wide at 265 front tyres.
I could probably get a recording of the sound, it's not a groaning or a whining type sound, not like it's cavitating. It just sounds like fluid rushing through a pipe or valve of some sort.

Yeah, I'm wary of a failure like that. There's a few times my car has stalled from a slightly rough engine and tune, and I've felt the rack forces without assist.

I'll have a look at that, see if anything is preemptively throwing codes