FFT showing evenly spaced signals when tuned to ~56 MHz down to 25.680
These periodic spectral lines look like they might be caused by something like a sparking power supply, DC-DC converter (for LED lighting or USB power, etc.), or high powered digital drivers running at approx. 150 kHz. You might want to walk around the house or neighborhood with a pocket AM radio to see if you can DF this RF noise (determine the direction its coming from). 

RTL-SDRs USB dongles based on R820T2 + RTL2832U also have a lower frequency limit somewhere around 52 MHz (where they go deaf or alias or won't lock).  26.68 appears to be near a folding point in the sample rate aliasing, e.g. right around Fs/2, where any spectrum plus its own complex conjugate can partially cancel.