News:
There is a knob at the left side for interior hood release, but it's not round like the vent knobs. Does the knob have anything written on it? I have a Holley choke knob that's in that general area, but it also has Holley written on it. Good advice from Mike to simply trace it back and see where it goes.
Go to the link and about 6 posts down is a picture of the rear speaker knob . . is this what you are talking about? https://forum.e-bodies.org/electrical-and-audio/11/rear-speaker-fader-switch-different/9393/
Most choke cables do not usually have a removable knob, but that doesn't mean that isn't what it is. You didn't say if there was a cable or wires coming out it. Whatever it is it is not stock if that was the intend of the question initially.
It's a small steel braided cable. I put a link to the picture but for some reason folks here don't seem to be able to open it. The heat is finally breaking here so probably Wednesday I'll get out in the garage and trace it back. General consensus at this point seems to be a choke cable that was added.