A normal full-contact graphene-substrate interface has been reported to have a thermal conductance in the order of 108 Wm(-2)K(-1). The reported work used a sandwiched structure to probe the interface energy coupling, and the phonon behavior in graphene is significantly altered in an undesirable way. Here we report an intriguing study of energy coupling across unconstrained graphene-substrate interfaces. Using novel Raman-based dual thermal probing, we directly measured the temperature drop across the few-nm gap interface that is subjected to a local heat flow induced by a second laser beam heating. For the first time, we determined the thermal conductance (Gt) as 183±10 and 266±10 Wm(-2)K(-1) for graphene/Si and graphene/SiO2 interfaces. This Gt is five orders of magnitude smaller than that of full interface contact. It reveals the remarkable effect of graphene corrugation on interface energy coupling. The measurement result is elucidated by atomistic modeling of local corrugation and energy exchange. By decoupling of graphene's thermal and mechanical behavior, we obtained the stress-induced Raman shift of graphene at around 0.1 cm(-1) or less, suggesting extremely loose interface mechanical coupling. The interface gap variation is evaluated quantitatively based on corrugation-induced Raman enhancement. The interface gap could change as large as 1.8 nm when the local thermal equilibrium is destroyed.