Unexpected peaks in spectral analysis
The large spike at ~9MHz could be some form of interference from electronics near the receiver or internal to the receiver (maybe from using a poorly conditioned power source).  My best guess for the spike at DC is a DC bias from quantization.  If the digitizer truncates instead rounds, the resulting digital signal will have a non-zero mean and therefore a DC offset.  We had this happen in an FPGA downcoverter implementation at a previous job.  Once they changed the FPGA to round, the DC offset went away.  If you have ever used an Ettus USRP radio, you see the same DC offset in many of those boxes.