I believe I found the cause of the flickering snowy picture that appear on certain TVs and receivers. Issue is fairly present. Many users on Sony support forums are reporting this.
PS4 => Sony STRDH740 HDMI => TV HDMI
In summary the flickering appears only when passing through the Sony STRDH740 receiver. Tried multiple cables, devices, TVs and all is working. Re-flashed the PS4 and the issue appeared as soon as the console was flashed to 1.51.
The flickering and strange snowy artifacts appear only at 1080p. Other resolutions don't display any problems.
Was on my Xbox One which is hooked up the same way and is working perfectly. Changed the TV Connection setting from HDMI (Auto-Select) to HDMI. This resets the resolution to 640x480. When I selected 1080p I was shocked to have the exact same effects appear suddenly ie flickering snowy picture and horizontal lines.
I looked over under Picture and saw that the Color depth setting was also reset to 24 bits per pixel. I selected 36 bits per pixel and like magic the picture is clear and flawless. (30 bits per pixel also works)
While I am not sure the meaning of the Color depth option I am now certain that it is a firmware issue and the the color depth on all PS4 must be by default set to 24 bits per pixel.
Now Sony can either introduce the other values depending on the set up in future firmware releases or they must give us the option to select it manually like on Xbox One.
Any more technical inclined mates out there willing to shed more light on this.
Can you help spread the word and hopefully it reaches Sony so they can investigate.
So in summary I am fairly sure that the problem with all the flickering snowy picture on certain TV and receivers is the Color depth. Sony needs to fix this asap and introduce the 36 bits per pixel option.