Doh! My PLLs lose lock. Crosstalk?

Besides looking for noise on the power supply pins VCCA and VCCD, I would next look clock input. I had a board which had clean clock source measured at the PCB board. However the clock input pin was picking up noise inside the device onto the clock signal. Check if any nearby IO pins are toggling by the clock input. If there is try to not toggle nearby pins to see if the problem changes. My solution was to use a different clock input on a different IO bank.