I haven't been around in quite awhile so I don't know if this has been covered. I calibrate my system with a RS analog SPL. Twice in the last six months, I've had the center and surrounds go exactly 3db down from the mains. I have the latest firmware update applied.

Has anybody experienced this?

Did the settings change? That's not something I remember hearing about or experiencing...

The trim levels were the same as when I did the previous calibration in both cases.

I tend to fiddle with my system a lot so I calibrate pretty often, but when I leave it alone for a month or so then check the calibration, everything seems to have stayed as I set it.

I calibrate and leave it. I check it about every six months or so.

So the levels were unchanged, but you found that you needed to bump the center and surrounds up by 3dB when you recalibrated? Did anything else in the system change in the interim?

The first time no. The second time I was getting ready to change out the center channel, but had noticed that dialog on a lot things seemed weak. So, I checked because of the first instance. So I guess that's no too. I'm now running Mackie HR824s across the front. I don't fiddle. I just calibrate and check it a couple times a year. Other than the Mackie upgrade the system has been the same since I bought the 990 in May 2006.