I don't have HD PRO, so I can't help you directly, but here are couple links where you might find aswer:
In one of these threads, rafgys is suggesting to another user this: "let me know if starting up without guitar plugged in, and waiting 30 sec- 1 minute to "warm up" the unit helps in your case at well (in my case, that seems to be the only way to avoid restarting the unit several times)"
hmmm....I think I would be powering up the other way around....HD PRO up first...then power amp...output supressed...recalling a patch does not clear the issue? wierd...I would power down in reverse...amp off first, followed by HD Pro...
I had the same problem on my Pod Hd Pro. The only way i lost this problem is:
Before you start the Pod Hd Pro, set the Master volume at minimum, and unplug the guitar cable (input)
Start the unit and wait around 20-30 seconds, the plug the guitar cable in. Hope this helps you.
I am using it like this for two weeks now and i had no problem. Before this, it was really fustrating, turning it on and off until it responded corect.
Hope this helps.
Reflash with the latest firmware? I have never had an issue with volume on start up and I just flip the power conditioner strip which turns everything on at once all the while my wireless or guitar is plugged in.