My air and heat have a strange smell when I use it.

I have a 2003 Trail blazer. This winter I smelled antifreeze whe I ran my heater. I had it worked on they replaced my thermostat , and a v.c gasket. they said I had no leaks. I kept smelling it. This spring it went away. Now I hear a gurggling noise under my radio and when I run my air it smells like a coffee smell.