Mark and all
I would think the source of such a noise would be from the 5V power supply rather than something within the Raspi as all clocks on the board ought to be stable. I will check when I get it working!
I am a complete novice on Linux I'm afraid.. I have just done the updates as detailed but no change
I have followed the Tutorial on the Airspy site and installed the RTL-SDR library but not AirspyHF one which I don't know how to do. (I am trying to use an AirspyHF+).
As for my version of hardware it says 2011 on the board. uname -a gives me "Linux raspberrypi 4.9.59+ #1047 Sun Oct 29 11:47:10 GMT 2017 armv61 GNU/Linux".
I don't understand what "Link" means on Prog's post!