I have noticed an intermittent loud 'thunk' noise from the front/dash area, seemingly only when the heater is on. It is fairly strong, at least to me, akin to the sound of what warping sheet metal (under temperature changes) may do (or a big spring unloading). Sometimes, there has also been a transient vibration, as if I have an ICE engine/transmission in front of me. Anybody else with the same observations? Anything to worry about?
Don't know what the thunk might be, but I have noticed the HVAC system does make a lot of noise plus the vibration. Do you get the noises without the car moving?
It is definitely not from anything placed loosely in the cabin. It does happen when the car is stationary but 'on,' again with the heater on.