I posted recently in the Carvin acoustic amp forum about this problem and in the course of investigating I discovered Caperfisherman's posts concerning the same problem I was having.
I purchased my amp in July 2014 and it started having issues Sep. 2016 I had taken it to a local amp guru that could find nothing wrong. It had been doing fine until last week when the "white noise" returned!
I contacted A Carvin tech that told me my options but at the end of our conversation he suggested that they may be able to sell me just the module (the "brain" of the amp) since my cabinet and speakers were not the issue.
So I called a sales rep and sure enough... A replacement is on the way for $191 shipped. I probably could have got off with $95 repair by shipping it to them, but I figure I may as well just spend the extra $$ and get basically a brand new amp. Here is a YouTube link where I was lucky enough to catch the problem on video!
https://youtu.be/N2nW1MmIszE