Strange clicking noise related to water supply

I have experienced a strange clicking noise coming from under my house. Not the banging noise I read about in other posts – this is not the sound of a pipe hitting a wall. It’s very hard to trace as it lasts only 3 seconds or so most of the time. One time I got lucky and was under the house while it was still going. It sounded like it was coming from the water pressure regulator and indeed there was a difference in vibration of the pipe on one side of the regulator vs the other. I tested the pressure and sure enough – it was at 125, which meant the pressure regular was no longer regulating the pressure. So I had it replaced. I thought the problem was solved. It did make a difference – the noise is no longer loud enough to wake me – but it does continue to happen now and then, albeit at a lower volume. Any ideas what could be causing this and how it’s related to the pressure regulator or water pressure in general? The new pressure regulator is working fine – I have it tuned to about 75.