To follow up on this... after no email reply from Wheels Manufacturing I ended up calling them directly and was - to my pleasant surprise - quickly routed to a knowledgeable tech there. He said others have had success eliminating similar creaking issues by removing the bearings with a press (from the WM outboard bb) and applying a small amount of Loctite compound between each bearing and the inner surface of the adapter before repressing the bearings (note: voids warranty, as to be expected).
I did this and it
almost entirely reduced the creak (tested over a handful of rides totaling ~200 miles), but not to my complete satisfaction. I then changed directions and installed one of these nifty
52g FSA BB30 English thread adapters, which came with its own little bottle of Loctite 609. For frames with aluminum shells or inserts like mine, this is a removable process with a bit of care and a hair blower.
So, here I am 1240 miles later and all is well. Zero honks or creaks of any kind, including when working extra hard out of the saddle or sprinting above 800w. Will report back if anything changes, but for now I am very satisfied.
A few pics from the install
