Cubase 6.5 Export Problem (use of Melodyne)

hi there,
i use cubase 6.5 under mac os 10.8.5

for our recent album i have all tracks in one big (!) project. at this moment i´m editing all tracks to send them to the mix. now i have the problem that there are artefacts and loudness differences on the export of the trombone tracks.
before i edited them with melodyne, but be careful with the use NOT to produce artefacts e.g.

the strange thing is that inside of the cubase-project the trombone tracks sound ok, meaning they don´t have any disturbing interferences.
now i remember that i recently recorded some violins and - without editing anything - the export had problems while the cub.-project didn´t !! also the violins have been exported from another project.
what the hell could this be? ;-()

thanks for any hints…