im on ubuntu 18.04.1 64bit and my lime mini is plugged directly into laptop usb 3.0 port
have 50ohm terminators on both Tx and Rx
i get the same thing you guys are in the pictures at multiples of 100mhz
https://imgur.com/SynOz6t
https://imgur.com/rEDBft7
https://imgur.com/dHgm5Ry