Did you try blowing it out with compressed air? (Duster)
I have a Dell 5100 that did the same thing several years back. I emailed and called Dell several times. The were 'surprised' as this was new to them... They offered 'advice', but their advice didn't help.
Weeks later, I finally found a forum with lots of people with the same heating issue, with the same Dell 5100. Someone suggested that the compressed air helped them. I approached mine from all angles and had very good success.
I know it's not the same model....but I'm sure it's worth a shot.