I'll try that

I would also compare the following:
a cup of the water from the source (tap?)
a cup of water from the portafilter (no coffee grounds added to the portafilter)
a cup of water that was steamed using the wand (heated to your usual milk temperature)

You'll probably want to cool the later two back down to room temperature for a proper comparison.

I've personally run into foul aftertastes when steaming milk that had added nutrients like omega3 and DHA, but it sounds like you already ruled that out with a variety of milk sources.

Drained and refilled steam boiler. Soaked wand and steam head for a while in rinza. Problem solved

Sounds good. Glad you were able to solve the problem.

Rocky

Thanks to everyone for all the good suggestions