Yeah, it could be a lapse in build quality. Either the fan has a defect from the time of manufacture, or perhaps there's a loose wire or something that brushes against it and becomes noticeable as the fan speed ramps up. You might want to make sure that it's not some other fan in your system having issues though, or a loose screw vibrating around in your case or something. Or electrical noises, for that matter.
be quiet! doesn't mean its a quiet psu - since APPLE doesn't actually make Apples : )
Actually, yes, that's exactly what it implies. : P The company's main thing is that they make computer equipment that's supposed to be quiet. Just look at their home page...
https://www.bequiet.com/en
"be quiet! - Silent PSUs, cases and PC cooling products."
"Enter the world of silent computing"
"Discover everything about the German silence experts"
"With more than 15 years experience in the field of noise reduction, be quiet! offers nearly inaudible products with quality on a world-class level."
And they advertise that particular power supply as having...
"EXCEPTIONALLY SILENT OPERATION"
"Achieved by a silence-optimized 120mm be quiet! fan"
"Airflow-optimized fan blades reduce turbulence, enabling best-in-class quiet functionality and the almost inaudible operation that be quiet! is famous for."
So, if the fan is in fact making an intermittent clicking noise, then that would definitely imply that something is not functioning as intended.