My Pro-V has developed a hiss. It was always there but it has become somewhat louder (or I just notice it and get annoyed by it more), but not so bad as to make it unplayable. But it is one of the reasons that I have been looking at changing the electronics (and burning the old ones in accordance with the dictats of Kat).
I don't have a correct answer, but my suspicion is that it is primarily the cheap pre-amp that causes it. And of course, it is gooped so that you can't troubleshoot it. I'm not sure that the pickups are great and in fact, I suspect that the addition of a preamp was probably to try to cover for weak p/u.