I personally find that a little strange. Perhaps it is because I never had my FF "Cranked up", but rather set to a semi-comfortable level (I've been tweaking it, but using the old DFP settings as a base guideline to start) - but mine has never started to "heat up" to the point where my Force Feedback has worn out. And I've used it in 6 hour long endurance races. No, I wasn't driving the whole six hours, but I was doing warm-up practice laps offline before hand for two hours, then I drove my three, so it was at least five. And everything was normal.
If it continues, you might want to call Tech support and ask them. Personally, if mine started to do that, I'd be afraid of it breaking on me