I've been watching closely smoke particles of car crash and heli crash. To me it seems like there's a keyframe missing in the animation loop of the sprite ( a morphing blob of smoke ) that's tied to a particle which goes from the emitter. It looks like a smoke sprite is transparent in a single keyframe of the animation which makes it flicker. Or is it maybe just that the first ,or the last keyframe is missing/is transparent from that loop animation, because it looks like it's extended 3x times or more ( probably so it can be seen from much further away). You can tell by the clusters of where the flicker are occurring, even though it seems random ,when it's really stretched out because of the wind, you can see the clusters. to me it looks like this :

It's really annoying to look at this because all of the other smokes look extremely good. And obviously Heli and cars are using the same emitter. It seems like the flickering is worse with Car engine smoke, because you've put more emitters ? So the particles are maybe also overlapping like layers because the engine is trying to calculate which one is closer to you ? or maybe because it's just shrunken down, the cycle is faster and it looks worse .

If this doesn't work, can you maybe use some of the existing ones ? like the black smoke grenade emitter something, as shown below.. smoke from grenades looks amazing.