Second I2C bus generating 60 Hz square wave at SCL

I have successfully implemented an initial I2C bus (I2C1) in my custom board design (using STM32F405).  I then added a second I2C bus (I2C2) to my design and have initiated it and set it up identical to I2C1.  The first bus continues to operate correctly (sending a clock signal out at 100 kHz).  I've specified the same clock frequency for the second bus.  However the SCL pin only puts out a *constant* 60 Hz square wave.  What could I be doing wrong?