Manufacturer's predictions of equipment noise output used in design are typically based on maximum speed or maximum design operating conditions. However, most modern equipment operates at variable speeds as controlled by building management software and the discrepancy between the "worst-case design" and the more typical equipment noise output along with resulting noise levels in occupied areas can be substantial. In certain cases, choosing one over the other can substantially change the noise control approach on a project. This paper presents previous examples where this has occurred, both in terms of submitted noise data and actual acoustical measurements at various operating points. The findings suggest that having clear definition as to the range of HVAC system operating points and reliable manufacturer's equipment noise predictions for the full range of equipment operating points are not only beneficial but necessary for making informed and cost-effective decisions regarding noise control on building projects.