In my Lexus, it's like a vault. No NVH, double thickness glass throughout, etc. So it's REALLY hard to hear anything. But I had a bearing go. It was REALLY loud droning. So I swapped it out. Quiet returned.
I wanted to see how damaged it was to create such a noise in my Lexus, so I took the assembly apart.
The abs sensor is integral to the unit. That pops off with some difficulty. Then a large nut, washer and dust cover. Inside, there are 2 races. The bearings aren't captive within the plastic carrier...they just sort of sit in and ride there. It was still packed with grease. Bearings and carrier all intact. They were all on size still. There was only, very, very slight wear on the walls...which I'm guessing was the source of the noise...though everything looked fine. For fun, I almost took apart the new one and swapped in ceramic balls but cost was a bit prohibitive so I didn't do it.