If the different counters use different fans, they may have different noise profiles/levels. E.g. the other counter may be using a higher RPM fan, etc. Or the grilles are causing the air to flow in/out differently, etc. A bit hard to say since the counters are not the same model.
The only way to tell if it's a dud is to compare with 2-3 more pcs of the exact same model. If the others are quiter then maybe yours is a dud. But it's also possible they all have the same hum.
The only way to tell if it's a dud is to compare with 2-3 more pcs of the exact same model. If the others are quiter then maybe yours is a dud. But it's also possible they all have the same hum.




