These are called images, and are a part of superheterodyne systems. When you take the incoming signal S, and you mix it with the local oscillator signal LO, you get 4 signals out: S-LO, LO-S, S+LO, S-LO. So if the real center frequency of your Lime is 2.5GHz, your signal of interest is at 2.4GHz, after mixing and digitization you will see a spike at center + .1GHz (signal - LO), center - .1GHz (LO - signal), possibly center (DC offset, aka “zero bang”). Now, in a complex mixer system like the Lime, hopefully if the in-phase and quadrature paths are totally symmetrical, the LO- signal part should be cancelled out between the two phases, leaving only the desired signal. If you haven’t done a calibration pass to balance the I and Q paths, you get what is known as “I/Q imbalance” and/or “I/Q offset” and you won’t null out the images.
Then there is the fact that if you have more than one signal coming in the antenna, those signals also mix and create sum and difference products. Moreover, since the Lime has such a broad, unfiltered front-end, the signals that are mixing may not be visible in the final digital passband, but are still screwing things up in the analog section before the A/D. This is one reason why it’s very good to have some form of preselection filter for the band of interest - you don’t want that flamethrower broadcast FM signal whacking your front end and distorting your 2.5GHz signal of interest.