Is it normal for my reciever to do this?
 

I have a Pioneer 'home-theatre-in-a-box' set-up, model #s:Dv-444 and VSX-C300 (reciever).

The question I'm wondering is lately the fan has been kicking on around the 90 min. mark of a movie. It does this for a minute or so, then stops. I know prolong use might make the reciever hot, but it does this more often now. I'm wondering if my HD converter is causing it to become more hotter than usual (it sits above the HD converter by about three inches and is separated by a inch thick shelf).
Or does for example, turning it on to watch an hour of extras features then turning it off, only three hours later to watch a feature length film causes it to become hot.
This doesn't effect the playability of the dvd player (separate from the reciever) or no OVERHEAT light shows up.

But is this normal or am I just a little paraniod?

BTW, it is a year old and I'm on vacation this week so the dvds are getting a little workout.

HD converter?

Do you mean HD receiver? If so then yes, HD receivers tend to run warm. It should probably be on top of the receiver.

Also make sure there's plenty of open space above, behind, and in front of the receiver. Don't put it in a closed cabinet!