I have made the same observation and was told, that if you reduce the gain to 40 - 50 the signal should disappear. In this case, of course, you need to amplify the LimeSDR Mini externally to compensate for the attenuated signal.
For my setup (LimeSDR Mini on 50 MHz to feed a BU500) it also worked to calibrate the TX-section of the LimeSDR Mini. in SDR Console, for example, you need to press the TX button and then, on the left side of the pane, press the „TX Calibrate“ button (be careful, you should disconnect the PA before calibrating to avoid damage).
Holger ‚Geri‘, DK8KW