Boy i haven't been around here for quite a while! It's good to get back...
I think Anytime is the right time for music! While you might not hear much (if anything) over the noises from the exhaust, i'm sure there would be plenty of situations when the car is sitting idle (at a club gathering, picnic, whatever) that some tunes might be just what sets the mood.
(the mood you seek is of course up to you...)
JD