I've encountered it a couple of times.  When it has happened to me I simply did a power off/power on cycle and it worked fine after that.

I have a Motorla EQ5 portable Bluetooth speaker that I use with my N7.  It works very well and provides better quality sound and louder volume then the N7's built-in speakers.  I've also used the speaker with my Motorola Droid Razr phone and Samsung Galaxy Tab 2 7.0 tablet with equally good results.  Motorola EQ5