Help. Mp3 mixdown to exported file has lower volume.

Strange.. I haven't mixed anything down in a while but I just worked on a project. I mixed it and tried to export audio (to Mp3) to play on my ipod and I notice the volume is really much lower than when mixed and played it in Sonar. Any suggestions as to how to fix this and why it's happening ? 
I have tried every which way to export this and still the same result. I even took out all the prochannel patches,  all effects, and softsynths.. I also tried only using Master bus outs and no sub outs..  I've tried bare bones tracks and I tried this all in every  possible preset in the MIXDOWN Audio dialog box.  Still I get an Mp3 with very low volume.  I tried older projects that mixed down just fine with older versions of Sonar tried them and still, I get a lower volume.  The meter in the master out bus is just kissing the red once in a while for moment so I know the volume should be good.  The outs on each track is set to Master and the Master Bus out is set to Focusrite usb 2.0 audio driver MON 1  the other choice is Focusrite usb audio driver HP which I think is headphones so I did not set it to that. However,  I did try that on one mixdown just to see.  Still not right.  What am I missing here ?  I know it's probably something simple but it's been driving me crazy for 3 days now.  Any suggestions ?  Thanks -   Brad 
  
I'm using a Scarlett 18i6 audio interface. connects to the computer by USB.  
Sonar X1 expanded  X1d build 535 x64
 
Core i7 2600 CPU @ 3.40Ghz Processor
Windows 7 professional 64bit
12GB Ram

Now I'm perplexed.   Yes, it is the same if imported back to Sonar. That's a good sign.  And when played in quick time it sounds fine too. However,  why is it so low in volume on my iPod compared to everything else on my my iPod and why is it so low in the iTunes player, and Windows Media player ?  BTW, thanks for your response.   Any other things I should look at ?   I'm going to try exporting it with the Master bus muted to see if it mixes down silent.    Thanks again.
 
 
Brad

I find the same thing. 
Everything maxed before export yet when I bring the mp3 into Audacity I find I can raise it 6 or 8 db without clipping.

I am not a iPod user. I am not an i-Anything user. So this is pure speculation...does the iPod support ReplayGain?

I don't see anything here called ReplayGain.   But, I will look at the iPod. Maybe you got it. Might be a setting in ipod that "fixes" volume differences  I dunno. Or a setting in iTunes.  I'll take a look.  BTW it even sounds lower when played on my computer. (Lower than in Sonar)  But, the "quick time player"  plays it the loudeset.  iTunes and Windows media player play it lower.   This is so wierd.  Every now and then something new (problematic) always comes up no matter how many years I've used this stuff. 

Replaygain on iPod/iTunes is called Soundcheck. See if you've got Soundcheck turned on.