Practically a laptop. Not sure what you are expecting.
Take it out of the case and slap a heatsink on it? Not really an ideal solution. I can't imagine the nightmare that mounting will be. Re-wiring fans to work with Dell computers isn't usually too big a deal. Typically they use a 5-pin connector, you just have to steal the connector off of the stock fan and your replacement fan and swap them.
You could maybe do something silly like liquid metal under there, that might make it cool enough for the fan to spin less. Also probably pick up a brand new fan from Dell, would be quieter than the original one I would think.