TMS320F28377S: Electrical noise on the DAC when I toggle GPIO bits

Part Number:TMS320F28377S

if I toggle GPIO0 while I use the DAC (to check my isr rate) I get significant noise on the DAC output.  Why is that?  How can I fix it so I can use both the DAC and the GPIO pins (the noise lines up with the GPIO transitions on a scope so it is clear that the source is the GPIO)?

Also, if I stop the GPIO outputs the dac works fine.

Thanks