Can you slowly insert the right side with no music playing and see if there's a small sound like something moves inside the unit? I just received my replacement pair and I noticed this driver flex type sound in only the right side. I've also sent them back as I'm not gonna take a chance on them like that.
I'm wondering if it's loose and just gets more loose over time from the pressure of inserting them and taking them out? You have to listen carefully to hear it. But the left side wouldn't do it at all for me. Only the right side.