What could cause dripping noises when I turn on my central heating?
My guess is that it's a vent pipe from your heating system that's resting against a part of the wood joist in your ceiling. As the vent heats up, it expands, and the expansion causes a dripping like sound as it slips and sticks against the joist. If this is the case, it will start slow when the heating cycle begins, speeds up as the hot air starts to come out of the vent, and then slow down to a near stop when the heating cycle has been going on for a while.

The same thing can happen with plumbing drain lines. I hear it all the time when the dishwasher dumps the hot water.