Smoke from Alternator area

I have a 95 chevy caprice with a 9c1 police package with a 5.7 liter engine. Car runs fine but one day last week it didn't start but started with a boost but batt. Sensor in the dash was low. After a while it started up fine and the sensor showed full charge then one day the sensor showed low power I checked it by Autozone and batt. And alternator were fine. However I noticed after running a while and the engine is turned off theres light smoke coming from the alternator area. I can't say it's coming from the alternator but it only smokes for a few minutes after the engine is shut never while its running. Otherwise everything is fine no warning lights or smells. Maybe someone can help me it would be much appreciated as I have no idea what it could be. Thanks