What can cause brief bubbling sounds/coolant smell when taking off from a stop?

What is your question?

So I just purchased a 2002 Jeep Liberty Sport (3.7 V6) from a friend and have had it for about a week now. Just the other day, I noticed a bubbling sound coming from the passenger side dash (guessing overflow tank) that comes and goes after I've been driving for at least 10 minutes or so, and it only seems to happen briefly when taking off from a stop. Haven't seen any indication of a leak just yet. Temperature gauge is normal and never exceeds the halfway point. Also, I can smell a coolant smell coming through the vents when this bubbling sound starts to occur, but it is not constant and seems to go away when I turn off the car. Guy I bought it from just had the radiator cap replaced and they flushed it and "verified proper operation". What could cause these bubbling sounds and smells if they don't happen every time I drive it? P.S. I obviously don't know much about the mechanical aspect of cars so dumb it down for me if you need to ;) lol