I've mixed a song down maybe 4 times tonight. I can play the project back perfectly and all mixes up to the most recent, which can be heard here - https://www.dropbox.com/s/tyzn06zk433o6d0/NDW%20%200519%2043.wav?dl=0
 
What on earth is that? I have no synths in this project at all, and I don't hear it when playing the project in real time. It's 44.1/24 dithered to 16. Oddly, it doesn't start as soon as the audio does. Thanks, Shep

sounds like some nasty digital distortion ... a few things to try to track this down:

• realtime bounce
• disable 64 bit option @ export
• export at same sample rate
• disable some FX at export and see if it persists

 

sounds like a short or a bad connection in the mic  cord...

Hi Shep,
 
Is "Fast Bounce" disabled?
If not, try disabling it.

Check all tracks and buses, make sure there isn't a plugin that you think you've turned off but actually isn't.  Remove all plugins you are not using.
 
This takes some time, but listen to each track soloed to see if there is a faint sound in each track that doesn't show up when the full mix is playing.
 
I hope you find it, the sound lurking