[slowmover]

For this very reason I made a pair of "stealth" earplugs. Take a standard "memory foam" type earplug, cut it down so the outer edge is flush with your ear hole, and color the outer surface of it black with a sharpie. I've worn them all day before without anyone noticing. They cut down the distant noise, but still let enough sound through to have a normal conversation with someone nearby.

And yes, I invented these shortly after my work area was converted to an open floor plan.