TFT display write noise
This is a difficult problem. Normally when you run a wide cable full of single ended signals with 1nS rise time, you can expect high supply/ground currents and high radiated noise. I am not surprised you can hear the video content on your audio.

Every EMC Engineer ought to have a book by Mr Henry Ott in their bookshelf. OK I don't, but I remember what he wrote back in the early 80's and it has served me well.

Let me recall some relevant topics.

Conducted Noise


Isolating Analog and Digital ground currents
Low ESR caps
multi-point grounds


Radiated Noise


Common-mode ferrite filters ( lossy noise absorption )
Shielding, shield termination and shield transfer impedance 
ground planes
optimal driving impedance
controlled impedance cable and terminators
interleaved grounds or twisted pair
standing wave effects


I recall the biggest radiation on ST506 device FCC testing was always the interface 50 wire ribbon cable.

If you were to pick the top 2 of each list and implement an appropriate fix, I would hope these will eliminate your problems.  If you use ribbon cable I would find a flat bar ferrite sleeve to absorb the radiating noise and locate it near the transmitting end or a clamshell sleeve just like on all VGA cables. The ferrite beads help on differential noise but not CM noise radiation. I think this fix is a must have. Laptops will usually have a flat ferrite layer somewhere over the LCD ribbon cable.

I probably missed a few topics but I don't believe buffers will help your issue unless they are ECL differential.