Apologize for my ignorance, I've been reading up on the DU problems and not sure if mine is related. My S60 @ 56k miles. I got it as CPO with 52k miles. Lately it seems the rear DU is really loud I hit 60 mph or more. It's literally like an on/off switch. Car is super silent at 59mph and super loud at 60mph and higher. It doesn't increase in volume with speed, just stays the same level of loudness. The sound is not the milling noise that people talk of. I can only describe it as an engine noise. Maybe it's normal and I'm just imagining things. Air and tire tread checked and they are nominal. Have a SC appt in 3 weeks but I like to go in slightly prepared with an idea of what it is. Thanks!