You are not the only one with this issue.
I got my Journey less than a month ago and I too have this issue with the volume coming up very loud at start up.
I think I have established a pattern. The problem seems to occur mainly when the source is the USB stick or the Satellite Radio. I have not experienced it when the source was regular FM/AM radio or the CD player.
Nonetheless this issue is extremely annoying and I will for sure ask the dealer service to rectify the problem.
The seat belt warning is also quite annoying, I am all for a warning signal but this one is a bit too much (loud and repetitive).
Stephen...