Something to do with muting his Radar detector below a certain speed?

Yup, that was it.

See, the only irritating thing about radar detectors is how frequently they give false alarms in grocery store parking lots. But if I muted the thing at speeds less than 30mph, then 90 percent of the false alarms would be eliminated.

Another fun thing would be to have it be selectable to either 30 or 65. When on the highway, I could flip it to 65 and then I wouldn't care about it beeping at me unless I was really speeding. But I'd be happy with just 30.

Regarding speed-sensitive volume control-- I still believe that an ambient noise sensor is a better way to handle that, because different road surfaces make different amounts of noise at a given speed. I could be going 100 on a nice road, and not need the music nearly as loud as going 50 on a rough road.