I'd swapped my P/S pump and let a whole bunch of air into the system, and was about to do this, and then realized it only takes an hour or so of sitting still for the bubbles to work themselves out of the reservoir.
So, I'd start it, work it lock to lock just once and leave it centered, then shut it off and wait.
In 3 cycles, the pump was quiet from lock to lock.
I believe the key was only working the wheel once, so the foamy stuff came up into the reservoir and stayed there.
1997 850 GLT sedan, 152K and WHOOHOO!
RIP 1996 850 wagon, 201K, hit by a runaway 4-wheeler
RIP 1996 850 GLT sedan 5spd, 260K, rearended someone
RIP 1986 245 boring, 200K, rusted beyond inspectability
RIP 1981 242 turbo 5spd, 300K, serious teenage crash