Knocking under power points to CV issues, and the fact that the joint is split means it is likely to be full of water and salt if you have been driving it in this filthy weather. I've had suspension, driveshaft and engine mount knocks:
- suspension tends to knock over bumpy roads, or when the car leans into corner. Never had suspension related noises on and off power.
- Engine mounts -you feel them more than you hear them. It also seems like the clutch is broken as it is hard to drive smoothly.
- Drive shafts, regular grumbling, worse under acceleration, will be worse under power and cornering in one direction. Starts off as a rumble, moves onto a clicking/thumping sound. If you back off the power, it goes away.