I’ve not had this experience. You may want to call Sonos Support directly to discuss it.

Especially since it is still under warranty.

thanks for the comments - I phoned CS, but after 35 minutes and no answer I gave up 

I was going to ask if these were the white or black models, as it may be a different coding.

I’m also wondering if there is a specific hair product you use, or sweat that could have broken down the coating.  Understandable if that’s not a question you want to answer.

You shouldn't give up. Sonos owes you an explanation and/or a replacement set. I’d be very P.O.’d. I’ve never had the stainless steel slides of a set of headphones degrade as shown  Of course all said assumes you haven’t done something to cause the degradation.

short hair, no hair product. 

it seems the friction of moving the ear piece up and down the stem ( adjusting to my head size, then adjusting back to compactness and storage) is scraping along the paint finish and causing the degradation…...and a handful of glitter 

It’s annoying that you have to adjust the size to fit into the travel case  A slightly bigger case would have allowed keeping it fully extended, for those who have big heads.

I would have appreciated a bit longer arms myself, it comes really close to fitting but another ¼ inch would have been perfect.

My case is off in storage for just that reason.

Same thing . I'm very disappointed of product quality  

I bought it 3 weeks ago.

I’m curious as to what Sonos Support said, when you called in?

Yeah…inquiring minds want to know?

Sonos CS didn't mention anything about product quality, past experience of this as an issue. just asked me to send the headphones back to them ( in Poland ) and then they would send out a replacement.

I wouldn’t expect them to have knowledge enough to speak to that, but at least replacing the errant device seems fair to me.