Usually the input is 50 ohms. And even after connecting the 50 ohm termination, you get these spurious signals and they are considerably larger, then it’s probably originated internally and that’s not a good sign. It could be problem with the LO, mixer, power supply issue and/or many more. It’s also possible that without good shielding it couples external noise. No SA is perfect so there are known spurious signals that will appear on the spectrum, but these are usually noted on the documentations by the manufacturer. I recommend you return it and get your money back if it’s possible.