We can hear a dripping noise (seems worse at night) starts really fast and then tails off, sometimes goes on for 5 minutes, sometimes 10 seconds and at non specific intervals throughout the day and night. We think we've tracked it down to the mains water pipe, as when we turn the stopcock off fully we don't hear the noise. It happens whenever there is no water running i.e. at 5am, 6am, 7am, but also an hour after we've ran a bath etc. It wakes me up :-(
Has anyone came across this before or does anyone have any idea what it might be?

I checked your toilets? Don't know if this is the sound you are hearing, but sometimes the flapper in the tank of the toilet doesn't seal well and a little water at a time seeps out until the fill valve senses the water is low and refills the tank and shuts off. This can be intermittent or all the time depending on the flapper sealing correctly. Example: someone uses the toilet. An hour later you hear water running for short time and then shuts off. Maybe it takes longer and maybe it seals completely and you don't hear anything. With the main shut off, then the tank can't refill, even if it is low on water. I have an ice maker in my fridge that I will hear turn on and off in the night sometimes. Just suggestions, maybe totally different sound than what I described. Water softeners also make a noise when recycling.

If this were a flapper leaking you were hear it all the time. My guess is expansion and contraction.and Knocking, popping, creaking and crackling pipes are a common complaint, especially in colder weather. I can tell you what's happening and take the mystery out of it but you're not going to like the repair. When a draw is made on a hot water line the line expands against a pipe strap next to a stud and when you drain hot water from your tub or shower it goes into a chase that is a little cooler then room temperature. The heat expands the pipe causing it to rub against the stud to which it is pipe strapped. This is the sound you hear. As it cools it contracts and the noise is heard again. To repair it you must tear open the walls and locate the pipe strap that's causing the problem and shim it tight. Most people when they learn what causes it just elect to live with it. Good luck and thank you for rating my answer. Tom