S/N Ratio Issues - Noise at -65 dB during "silence" after file export [SOLVED-sort of]

I would certainly look at your interface. The best way to test this is to not use the Zoom. 
There no reason you cannot switch to your on board audio and use WASAPI exclusive mode for just an export. If you have any other ASIO interface kicking around or a friend  or music store near by all the better. But I have been using a Laptop and it's on board audio system for a year and my exports are just fine. I load them into Wave Lab to master and I would certainly hear and see noise in my first 2 blank measures. 
 
Does this happen with every project or just one? 

Ya I'm actually not dead sure on how things work as far as the audio inside the box goes. It is I would think only the driver involved and not the hardware, that I'm pretty sure of. The audio from your DAW is basically just ones and zeroes and exporting is a matter of  tossing them together 100% digitall and the only place noise could be introduced that I can think of is a plug in but why would that happen Nobody would use that plug in. 
So if an Audio driver can cause noise using a different driver would suss that out. 

I thought you guys must have nailed it - a plug-in.  Helix Native on two buses in my current project.  I've used it in every project for last two months since it came out.    But NO.  I tried disabling that and nothing changed.  I then disabled EVERY FX plug-in, ProChannel and soft synth -- both on mixdown and on export.  The same problem persists.  So perhaps it is the interface.  I've been trying to avoid crawling around behind my racks and on the dusty floor to rearrange wires, but I guess I have no choice.  I'll let you know if that changes anything.
 
Thanks very much for your suggestions, however.
 
Aloha,
Bill
 

hello friend,.
usually, noise is coming from pre amp area, microphone and the like, guitar pickups,. there is a great program called acon digital media or suite or something to that effect, something, i cant remember now exactly , it is 4 plug ins , one is noise reduction and there is another 3 plug ins, one is for recurving the tops of any peaks that have been clipped.
it is kind of hard to get used to how it works tho,
you have to mess with the knobs and see what they do to the existing material.
like set them and then apply effect and look at the result then try somthing else if that doesnt meet your expectations, it is really good once you get the setting rite,.
it is not allways the same for every track,
there is a listen to noise command where you loop the noisy area and allow the machine to see the signal that is trouble.
so acon digital media ,. that i heard of on this web site ,the guy who wronte the book on SONAR, Scott at digi freq, it was his post years ago.
it is special program for cleaning up noise off of tracks, i usually never use dithering and a allways endu up with good mix down result.
16 bit can not go any lower then around 90 or 96 db depends. at 96 dB that was better then cassette tape or any other kind of magnetic tape.
i have never used a zoom tho i did look at the hi end zoom picture camera that listed specs of a 120dB of dynamic range,
and as far as i know
the machines run on battery,
pure dc power supply,.
usualy the power suuply is the source of noise.
im having a trouble with noise here now,
so bad in fact i stoped recording and went shopping for an oscilloscope to track down the source of it,.
looks like it is my 120 v supply,. it is so bad that the dc power supplys in my computer and
audio interfaces are being hit, it is so bad that it blew up my audio interfaces, 2 of them.
the scope is digital, i have never used a fully digital scope and it has a learning curve similar to SONAR.
learning surce slowing me down, read the manual.
but , having used the scope yesterday and today,. i can see very very bad power,.
aware of what it is now, im reasonably sure anyway, it is a battery backup for 120vac.
im in a large place with many rooms and many people pluging in all kinds of various things into the ac power so some of that could be the source too.
very hard to reach the battery backup, stashed underneath, i have to disconnect the old unit and try again
noise is allways an issue for everybody,.
i mean if we use 16 bit with 90dB of dynamic range and we turn up were going to hear the bottom end which is not usually all zero's code combination.
so, noise gates are good too,
and so is manually delete the quiet portions using fades, ins and outs.
manual actually beats all others but takes the longest amount of time, from what i know from doing.
many years ago, i did a mix down with dither and without and listened to the result
i did the same thing with every kind of dither that SONAR includes .p o wr or whatever they call it.
im not going to tell anybody how to make "their sound" but me,. i decided not to use dither.
there is an option under audio preferences to turn off dither so it wont be used at any time and thats what i allways have it set to,
and i dont have any troubles, usually, when my AC power supply is not faulty.
SONAR has lots of information on what dither does in the help files,
however, nothing says it better then listening to it with your own ears

im trying to post a request to include an option to to export a copy protected file but having a time of learing how to get around here,i dont post comments hardly ever.
FYI
i been using SONAR since 2006 pretty much every day for the most part
SONAR allways changing , improves. very good now.
later friend
Wayne

can you repro this on an "empty" or new project?

What's the noise level if you disable dither? 

I stopped using Dither a while back, All my exports are 16 bit and dead quiet. Whatever dither can do to imporve my songs it's not worth the bother.