MacBook Pro Early 2008 Fan running while in standby
It would make sense from my point of view to look for a certified Apple Service Provider or Apple Retail Store and ask them about replacing your Mac thermal grease. Chances are they offer this in a sort of "spring cleaning" program. Over time the thermal paste between your CPU and GPU and the heat sink dries up and doesn't do what it is suppose to do. This can happen but doesn't mean it is, sometimes the fans just get full of dust and need to be cleaned out. The important thing is just making sure the mac is getting good airflow and that its vents are several inches (6-8) away from anything that could be obstructing airflow.