Hiss when bouncing soft synths

I have a track with a soft synth (in this case, Omnisphere), and I used the "Bounce to Track" function to make a seperate Audio track.  The soft synth track started at bar 2, and I noticed when it had exported, there was some activity in bar 1 - I pulled the Audio WAV into Sound Forge and that bar 1 was flickering around -80db.   I normalized this bar, and it turns out to be hiss.   That shouldn't be happening should it, when I'm working only with in-the-box sounds?    Any ideas how I can trace the source of the hiss and fix it?

Thanks for the tip Jim.  i tried with "fast Bounce" turned off, but same result.    I fiddled with a few things - in this case I have Ozone 5 on the Master Bus - when this was ON I got the hiss, and when I turned ozone OFF, then it bounced fine without hiss (with or without "fast bounce" ticked).   I've no idea why having Ozone on my Master Bus would have caused this?   Can it be a computer power issue ... or something else?

In your Ozone 5 settings: Is there a dither active & what word length? Is there a console emulator? (I don't know Ozone 5, just guessing)