There were times when the carrier and IBOC sidebands were on the air. It did come back at 3:00 AM, as I was driving back from Metro airport. I heard it announced at 11:57 PM that they would be signing off at midnight for transmitter maintenance. Several people reported drop outs in modulation in the days leading up to the maintenance. I'm thinking that it was probably boards that control the modulation level that were going bad and had to be replaced. A soft tube might have been intermittent and do that in the old days, but isn't their transmitter all solid state? The thing that surprised me is that they wouldn't have just used the back up transmitter if it was transmitter issues. But the IBOC probably complicates that, and as I said, they were running the IBOC when it was on with the carrier during the silent period. So I guess they could have been doing impedance bridge measurements on the directional antenna system and such also.
I tried to hear stations on 940 and 960, as well as 950, but only once did a clear signal arrive on 960, probably from WDBJ/WFIR Roanoke. Mostly it was the low level of numerous RSS interfering signals to well protected stations.
Thank you, WWJ, for keeping me awake while driving! Both the transmitter maintenance and DXing on 940, 950, and 960, and the programming after 3:00 AM kept me alert.