Engine coolant does have a distinct 'sweet' smell to it.
It is possible to have a small leak in the heater core that is just enough seepage to make the noise and not enough to be noticeable immediately on the coolant level.
It will be a good idea to inspect the heater core for any leaks.
You can also do a pressure test on the cooling system. On the pressure test the cooling system gets pressurized with a tool, and if there is a leak; the system will loose pressure and that will show up on the gauge.
Here is a helpful video showing how to do the pressure test:
I have attached diagrams for the heater core below.
Please let me know if you have any questions.
Images (Click to enlarge)
Tuesday, November 30th, 2021 AT 9:36 PM