Onkyo Speaker Burning smell

[rkproceed]

I just purchased an Onkyo HT-S5305 Htib

it's supposed to be a homogenous package , the receiver supplies a 100 W/Ch and the speakers are all a 120W max power , when I raise the vol more than 60 of 80 , the center speaker starts making a bad smell like plastic burning.

what the issue might be guys ?
Tzanks