There is a phenomenon called 'beat frequency oscillation', which is a property of wave mechanics. (Unfortunately the Google search findings mostly relate to radio frequencies, where the phenomena is utilised)
Nevertheless, as lectriclegs indicates above, if you have two sources of flickering which are close to each other, in terms of both proximity, and frequency, then although each of these may flicker at a rate that is above your capacity to visually detect, they produce a resultant (beat) which is at a much lower frequency. ie one which you may well find detectable.
It is the same phenomenon as the beats you can hear when you are almost on target when tuning a stringed musical instrument to a reference pitch.
To understand it in non technical terms, every so often, the maximum light output of the flicker from both bulb and TV combine, and mid way between these additive peaks, similarly the lows also combine resulting in the flicker that you can see.
A slight change in frequency may well make the phenomenon disappear, but as I doubt you will find the information concerning this for any particular bulb, I would guess that you are in the land of trial and error.