Can you give it a dusting with canned air and a gentle soft brushing?

If it isn’t eternal dust then I’d send a picture along to Sonos Support and work on a replacement.

Thank you I’ll give that a go.

I did send a picture to Sonos support and they said as it is not a manufacturing issue it isn’t covered by Sonos

The way light can reflect off the grill can make it look like a grey patch has formed.

if you move the speaker, does the patch also move/disappear?!