How to reduce fan noise with some latest Dell laptops, Desktop PC's?

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http://askubuntu.com – I have a few new Dell laptops and desktop PC's. Some of them have extremely noisy fans. The technicians who are sent by Dell refuse to attempt to fix things when they see that the OS is Ubuntu. They seem to be comfortable dealing with machines running MS Windows. For Linux, is there any way to slow or lower the fan speed? Please can anyone advise how it should be done. I have tried lm_sensors but failed. (HowTos)