The gains set-up is unusual on the VX2000 for two reasons:
the VX2000 mic on the camera is unusually low-sensitivity,
and the gains and AGC are set up for it; the AGC is
different from others and "quiets" audio more than others,
with more than usual headroom retained. Switching "straight
across" to manual makes manual sound noisier, but matching
levels for not clipping, and especially if a higher-sensitivity
mic is used (most are), the noise goes down. The noise level
is not as low as the 16-bit format would allow, but it is low
for consumer/prosumer cameras. PD150 folks are generally pros,
and demanded better performance. Also, the headphone amp is
noisy, and it also exaggerates the high end - and most
monitoring headphones are high-end rough and peaked, making
monitoring this way unrealistic for noise evaluation, especially
if the inputs are not loaded. The VX2000 gain range is very
wide, so someone turning up the gains to "hear the noise" will
hear lots of it, though this is NOT a realistic test.