The cooling fan inside DM800 HD (mine is clone, but I heard the original is the same) create a great sound, very annoying especially at night. After many attempts I have found a way to remain cool that sounds is acceptable.
Materials include: 01 fans RedWings50 AIREN FAN (2.5 EUR),01 Noiseblocker PCI Single Channel Fan Speed Controller(2 EUR)
Start Now
1. Remove the fan attached to the motherboard (please note this is a fan blowing wind down. Because like so even if operating at full capacity (very loud sound) after about 30 minutes, then hangs box)
2. Remove the modem (no need to use this)
3. Remove the fan controller out of the bar PCI.
4. Add fan (AIREN FAN RedWings50) into the HDD tray, note this fan blows UP.
5. Fitter Fan Speed Controller into the position of the modem.
6. Plug the power supply for fan (Fan-Fan Speed Controller connected continued)
Now you try from Lowest levels to higher with an adjustable knob from behind machine.
Biger fan is better, of cause best fan is.... better!
Sorry my English is very bad, Google translate - the same!
Good luck!