You might want to compare before you switch. At a quick glance, VTEB beats BND even in the 10% tax bracket. With yields at historic lows, lower duration means a smaller loss if/when rates go back up.
Vanguard Tax-Exempt Bond ETF (VTEB)
1.09% SEC yield, 5.4 year duration
Vanguard Total Bond ETF (BND)
1.16% SEC yield... 1.05% after tax?, 6.5 year duration