If the machine's compressor runs when you switch it on, then turn the machine on maximum and let it run for an hour or so. Then check the coils in the back with your hand. If they are not getting cold at all, then there is a significant problem with the refrigeration process in the unit. It may have developed a leak and allowed your refrigerant gas to escape, or there may be another internal problem with the compressor. Either way you would need to have it serviced by a fridge technician, or more likely just replaced with a whole new unit since both options can potentially cost about the same.
If the unit runs normally and the coils are getting cold, then make sure they are not totally icing up which will impede the unit's performance. If your dehumidifier is freezing up then that probably means the unit itself is actually working well. The temperature or humidity level in the room may be a bit low and you may have the unit turned up too high for the conditions.
Try turning down the setting on the unit so that it cycles on and off every few hours and does not run continuously.
Also try using some warm soapy water to clean off any dust or oily residue from the cooling coils in the rear of the unit. Remember to also clean the air intake filter while you are at it.
If the ambient temperature in the room is a bit low, you can try adding some heat to the room if necessary. A dehumidifier will not work properly if the ambient air temperature is too low. Generally, the warmer and more humid the room is, the better they work.Since warm air rises, you can even try lifting the unit higher up off the cold floor onto a bench or table where the air is warmer.
You can click on the following link for a general operating and troubleshooting guide with additional tips on effective dehumidifier operation:http://www.allergyconsumerreview.com/dehumidifier-advice-troubleshooting.html
The rattling noise may just be the coils vibrating against each other. Sometimes you can gently bend the coils apart slightly so they don't rattle, just dont bend them too much or you might damage them.
I hope that was helpful to you, good luck.
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