I noticed this carrier appear on 1670.004 at 2258 UTC using Carrier Sleuth, it went QRT 0637 UTC. I don't expect a licensed MW station to sign on or off at these times, so I suspect it was a pirate.
Using Carrier Sleuth to find a few times when the signal peaked, I listened to the SDR recording at these times using mySdrPlayback, which also displays the exact carrier frequency of the strongest station as you listen, updated each second. I did notice another station fade in at these times right on 1670.004 kHz, playing what I'd describe as current YL pop music.
