I've actually had a bit of intermittent trouble with FW11.03 unfortunately... No big deal, I'm back on 11.01 at the moment, but thought I should let you folks know.
Basically, it sometimes sounds very thin and clean with noticeably lower output, like I've turned the volume knob way down on my guitar (e.g. Brit 800 preset is very clean, Euro Uber has only slight breakup), and there's a lot of background noise. It doesn't happen every time I turn it on, but very often. It happens whether I'm listening through my studio monitors or headphones. I noticed in the Utility->Status menu that when it's happening the L1 and R1 output levels are showing a lot of output (over 50%) with the guitar volume rolled off, which doesn't happen normally. Power amp and cabinet modelling are both on.
Sometimes it seems to go from good to bad when I change leads or guitars, but I have checked all my leads and guitars, and they all work consistently with other amps, and there's no consistent pattern of which one(s) sound good or bad, it seems to be more about plugging and unplugging.
So, I reinstalled the FW and presets and cleaned the system settings (following the instructions on the Wiki), but no luck. Then I reinstalled 11.01 and everything was back to being amazingly awesome. I tried reinstalling 11.03 again and got the same results (sounding wrong most times I turned it on), so I went back to 11.01 again and everything is great again.
Any other troubleshooting ideas? I'm using a Strat and plugged into a Mac running 10.7.5, driver and Axe-Edit are up to date.
Cliff - if it's just some unidentifiable gremlin I'm happy to wait till the next FW update, otherwise if there's anything else you'd like me to do just let me know. Sorry to be complaining about an easily avoidable issue with the greatest piece of gear I've ever come across!!