New Mac Mini Server Causing APC UPS To Click

just hooked new 2011 mini server apc back-ups es 750 , apc unit won't stop clicking. sounds continually switching battery backup off , on. 2-3 times minute. unit used on pc year no troubles. started since plugging mini it. nothing new has been added ups other mini. ideas?
thanks!

 

is else plugged ups?

 

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