The 3rd harmonic of WWL 870 would be 2610 kHz, so it is not that.
The 8th harmonic of WWL 870 would be 6960 kHz, but you are reporting a frequency almost 10 kHz away, so probably not that.
I imagine that you receive a very strong signal from WWL on the fundamental considering your location. Does your loop have an amplifier? Could this be overload? A mixing product?