My phone hates 2G + Sd Card
I would indeed verify first that this is not related to some 3rd party app or any other than stock ROM. For this do a complete reset and try again. Also try with a smaller SD card since 16GB might not be supported by your phone (need to check specs for that, I don't know).

You can make a backup to get it back to your personalized settings quick. 

If you can confirm the stock ROM and default settings do have this bug too you can report this to HTC. Otherwise you'll have to solve it on your own, looking what app/setting is getting this result.