Hiss is common in crappy ANR headsets. I have a £80 Sony headset for walkman type uses, or for wearing on an airliner to keep the noise down. It whistles too. And my GF went for one of the free trials of the £300 Bose ANR headset which they are trying to flog to airline passengers etc; it was very comfy but whistled too and was sent back, and Bose said nothing whatsoever...