subwoofer wierd noise and only coonected to 1 voice coil when it has 2


hi i just got a new subwoofer its a megavox viper series vas-dd12
you cant find any specs online but i know its dual voice coil 4 ohm subb
its connected only to 1 voice coil not to both of them
so i wanted to ask if that rattling sound is regular in a subbwoffer you can barely hear it or maybe  its because i have only one voice coil connected
i have it connected to a  Boss Chaos Series C600 car amp its hocked up to a pc power supply and its working great
so i just want to know if any one can tell me if that rattling sound is normal or something the subwoofer looks like its working fine just to be sure 

and another question is it ok for the subwoofer to work on 1 dual voice coil when it has 2 

very important please help appreciate it:) 
edanawad12
there is nothing touch the sub this sounds become when i make the sub volume high so i want to know if its normal or not 
and the subs model : megavox vas-dd12 
Rattling sounds are seldom normal or fine. What exactly is it that's making the rattling sound?