I would guess so because there should not be an odor coming from your vents and if it is worse when the heat is on there's a chance something literally crawled up there and died! I always wanted to say that not referring to peoples butts. lol But all kidding aside. You would be surprised at the little critters that can find there way into your venting system. Or just organic material that has gotten in there somehow and decayed. Best of luck tracking down those oderiferous emanations.