I'm a bit late replying, just stumbled across this.
I have a Fuze+ as well. Rockbox has "issues" but still better than Sansa's.
The black screen - I have had a few times. I think that the unit is still ON, but is displaying Black/Nothing. I do same as you, hold power down for 10sec. or so, then restart. Fine after that.
Noise when turning On: Yup, on mine it is painful. I do not put the buds in my ears until RB has finished booting. The initial squawk! sound like someone plugging/unplugging their guitar into an amp at high volume.
After boot, there is a bit of background noise when still on the Home screen, but disappears (or is no longer noticeable) when playing music. Sounds a bit like static, or even a HDD spinning. Weird. Might be related to the CRT-like screen flicker when powering on?
Battery - Sansa lies. Battery (in my experience) won't get you anywhere near those numbers. Even when mine is turned completely OFF, the battery drains over a few days. Don't know where all that juice is going, because it certainly isn't going to the (useless) clock. It does NOT keep time when powered Off. (with either f/w)
On the upside though, actual music thru' the Fuze+ is pretty decent, OF or RB f/w.
If I could find a second 16GB one in town, I would still get one, now that I have (mostly) figured out the quirks.