There are several possible causes. A few ..
1) You have the control room volume jacked up. The export will be at the "master out" reference level, not the Control Room Level.
2) You have double bussed the Control Room and the Master Outs, so you are hearing things twice as loud
3) You are doing bit reduction on the export
There are more, but those are the typical.
HOVER HATERS UNITE -- DOWN WITH HOVER
cpu:i7 980x - RAM:24gb - OS:Win8.1x64 - Interfaces:Lynx Aurora, Komplete Audio 6 - MIDI:Midisport 4x4, Quadra Thru
Steiny Suff: CMC:FD,CH,TP,QC,PD | Wavelab 8 |Cubase 6.5/7.5| H5, HS2, HSO, Padshop Pro