It is very unlikely that you have any anti-freeze in your fin-tube baseboard and even less likely that you would smell it unless you have an active leak. If you had anti-freeze it would most likely be propylene glycol which is generally non-toxic even food grade- and if by chance you had ethylene glycol (common in automobile anti-freeze and commercial boiler systems) in your baseboard fin-tube, you would have to drink it to be get sick and yes it would be fatal for a cat or dog.
I would suggest that the smell comes when fin his hot and therefore is coming from the outside of the fin. Something on or near the fin is off-gassing, say the carpet below.
Important note - I'm not a pro
Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014
Now get some chickens, feed them on compost, and get your health back from great eggs from that sick building syndrome.
I'm sure it's ethylene glycol heat-transfer fluid. It's commonly used in heating applications where the temperature in the heat transfer can be below 32F. It's the most common antifreeze solution for standard heating and cooling applications. However, it should be avoided if there is any change of leakage into food processing systems or portable water. If that's the case, it's strongly recommended to resort to propylene glycol.