Evidently something is happening. Have you tried reformatting your MicroSD?
Yep, tried it with multiple different mSD cards, including freshly formatted cards. Literally, we battled this issue for 8 months on the SP2 until Microsoft finally issued a firmware update end of May that was included in the June round of updates. Still
shocked they let it return on the SP3.
Only somewhat reliable solution I've found at this point is simply don't insert an mSD card.... although, just like on the SP2, others are reporting this occurring without ever inserting a mSD card.
For further info, search the SP2 forum here or on answers.microsoft.com, tons of posts regarding this issue, but unfortunately no solutions. I can only hope Microsoft decides to fix it sooner than the 8 months it took them last time...
Unfortunately, most people don't even know it is occurring when it does, as extra heat and diminished battery life are the only signs unless you constantly run a process monitor (like I've learned to do!)