It sounds like what you are seeing is normal and there's no ill effects from it. I'd only worry about it if it becomes really loud, which means there's some problem with the fan. That 'loud' has different meanings for different people. I don't think I've even heard the fan running on mine. Of course, it's stuck away under a seat so I wouldn't expect to hear it. I also have a '710 (same radio just a different head) within 'hearing' distance in the house. Never heard that fan either. It's detectable, sure, but that certainly doesn't mean objectionable. If heat really worries you, put the thing in the fridge. Just remember to defrost it occasionally...
- 'Doc