When the car is warm, the hot start assist grinds when starting after the engine is warm (doesn't do it when cold). It's really annoying, but still fires up every time. Is this something I need to worry about? WHY does it make that horrendous noise?

 

Not sure why the noise, but just do what everyone else does, toss it. It has no useful purpose.
It is apparently the appendix of an RX-7.

 

just unplug it my 79 did the same thing

 

Same here.

I unplugged it 6 months ago because it was making grinding noises and found that the car actually starts better and easier now when cold or hot.

 

Yeah, the hot start assist has gears that go out and just grind, so most likely its not doing anything anyway. Just remove it or unplug it. Mine started just fine without it, and when I took mine out, it still worked.

~T.J.