A whiff of anti-freeze comes from a very small loss of coolant. You can probably go for years without noticing any level drop, but it will most likely NOT heal itself, so if you plan to keep the car, you should probably fix it. Oh - it is more than likely a leak in the heater core. It could be the hose connections at the firewall, but more than likely not. you can probably try some of the stop-leak additives, but use them with caution - they could crud something else up.
Never done one on the Equinox, but with my Maxima, I had to pull the whole dash out, and it wasn't fun. Likely I picked a nice fall day, so at least the weather was nice.
2018 Equinox LT1 1.5 L 4 cyl, AWD, S/R Cajun Red Tintcoat/Black
2010 Equinox LTZ 2.4 L 4 cyl, FWD, S/R Cardinal Red/Black