- it's was very quite and I hear a small whirling noise for maybe 15-20 seconds. Then it does it again in maybe one minute, it always does that, I have the key fob in my pocket.
We have noted the "noise", which is not unlike the sound of the spinning CD, a part of the NAV-system in our last car. When the NAV CD was not inserted, the system did search for it at - intervals.
I don't know for sure what is the origin of "noise", in the GLK, however does unlocking the vehicle start the "preflight" (preparations) of it. A part of these are making the Audio, whichever system is installed, available for use. There is a controller incorporated in the system, so maybe the "noise" is a fan or a laser seeking for a CD etc.
- and would it eventually run the battery down?
Not this electrical-/electronic circuit alone, as this
particular circuit most likely is not active when the car is locked, which could be confirmed by locking it while sitting in it. NOTE: The Anti-theft alarm systems on the European market have an Interior motion sensor
which can be deactivated
by a switch, before arming the alarm.
with all the other (small) sources of battery surge / "drainage" at standstill, its internal surge included, it reduces its capacity over time, given the ride is not frequently "taken on a spin". Faster during cold(er) environmentals, which is the reason why we have an integrated battery charger to "refresh" the battery from time to time. That is good practice for its longevity as well.