Yeah I agree, listen to your body.. Some of us can run every day without problem, others have a really hard time and lose muscle mass.. 3 miles is only a short jaunt really, so there shouldn't be any harm..
I always chuckle when I get big muscly guys tell me than I'm doing too much cardio.. I'm sure they would if they could, but they have to lug around so much fat that they end up injuring themselves.. once you're in the groove, injury isn't much more of a risk than 4 times a week, and if you eat properly you will stay anabolic..
I still have pretty decent size, great conditioning, and those "big muscly guys"shut their mouths real quick when they see my ripped abs.. I'd rather be fast and strong than just "big".. If you are just big, as soon as you turn your back on diet/training, you will turn into the human blob..