I've been having this problem too since July 2011. It went away for a bit after a reformat. It came back a few months ago and has been driving me insane. I use my XPS 15 for graphic work while at work which uses the dedicated graphics card. Once the card goes above 60C, the fan keeps revving up and revving down every few seconds for hours. Even if I let the laptop cool down to below 60C, it keeps going crazy. Including when I shut down my work programs that use the dedicated GPU. Even putting the laptop to sleep and turning it back on barely worked any more.
This has distracted me from focusing on work. All I can focus on is the pulsing. It's like Chinese Water Torture...That I paid for!!! The rhythm of the fan gets into your head for hours, then will suddenly stop. But every time you use your laptop, you're wondering when it's going to start again.
I can't believe there isn't a recall on units affected by this. This is a huge annoyance.
I paid $100 extra last week to get the onsite warranty, just to have a tech come and check out my laptop. He replaced the fan and heatsink yesterday. There was a fair amount of caked up dust in the heatsink vents and fan. I am now idling in the low 50Cs now and I have all my work programs open. I cannot hear the fan...thank the lord.
That being said, I did install a program to check my GPU temp and that caused the pulsing to return. It went away though as soon as I closed it.
One suggestion to you, that won't involve using workarounds to cripple your laptop, is to open up your laptop and clean out the dust and possibly re-paste the heatsink. My temperature right now is 50C, with a bunch of programs idling, well below the dreaded 60C mark.
And to DELL, wow I just can't believe it's been over a year and a huge company like you still hasn't fixed this issue or at least given us answers. How could you do this to us? Why can't we just exchange for a model that doesn't have this problem out of the box? Doesn't that seem like the right thing to do? Give us something that works like it should. If a car had an AC/heat problem that went on and off like this, guess what? Recall!