Cross talk!
Crosstalk need not happen only due to mutual coupling. Along with the AC effect, there is a DC crosstalk component also. This is due to sharing common ground and supplies between various blocks. Sharing common ground means that any change in the current in one block results in ground level change and hence affecting another block.
Mainly layout techniques like reducing coupling by placing current carrying wires far away, inductors far away and having different grounds for different blocks, connecting grounds and supplies only at the pads are used to reduce crosstalk