Noise, Temperature
The 135mm fan is barely heard at low loads. The confines of the chassis and 1,000W power output are always going to lead to a noisier supply when at full chat. Run it at 750W or so and it remains reasonably quiet.
80 PLUS Bronze certification inevitably leads to extra heat being generated in the transformation of current. At 1,000W there's a significant amount of extra heat that needs to be dissipated. The consequence is a warm PSU.