Electrical – Water hammer or something else

I'm having a bit of a mysterious problem. A couple of weeks ago I've replaced a dimmer switch in the upstairs bathroom. Of course while working on that I shut off the electricity for that part of the house. Since turning it back on we've been hearing this thumping sound which seems to be coming from the ceiling. The sound is extremely frequent: I've timed it and it's exactly every 2 minutes and 53 seconds.

At first I didn't link it to that dimmer job, because I thought it was water related (like water hammer). But after a couple of days of being annoyed with the sound I've decided to turn the electricity back off (same circuit breaker) and suddenly the sound stopped.

I did notice in the garage where the water comes in that the pressure was too high so I've already adjusted the pressure regulator lowering the pressure, but the problem persists.

I've also bled the water pipes using this info here: http://www.factsfacts.com/MyHomeRepair/PipeNoises.htm

Quote:

Turn off the water to the house at the entry. Find the lowest faucet
in your house–often this is an outdoor garden hose faucet–open this
faucet and then open a few of the indoor faucets at high locations
such as upstairs or at a wet bar and let the low faucet drain for 5
minutes or until it stops dripping, whichever takes longer. Close all
the faucets and turn the main back on.

I suspect it has something to do with the fire sprinkler system. When I turn on the circuit breaker switch in the box I do hear water running, or so it seems. The only thing I can think of would be the sprinkler system.

Does anyone have an idea or pointer of what this could be? At this point I'm not even sure if I should call a plumber or an electrician.

Edit
I've tried to record the sound with my phone, because it's hard to describe. Unfortunately the quality of the recording isn't great – the mic of the phone is unable to capture the full frequency spectrum. It sounds a lot louder and deeper in real life and I can actually feel some vibration in the floor when it happens. It sounds mostly like the sound of impact, what I would imagine a poltergeist to sound like.
Here's the recording, you can hear the sound @ 0:18

Sound recording

Edit 2
As suggested by Tester101 here's a list of items on the circuit:
– Two wallsockets in the master bathroom (not being used right now)

• Possibly the control unit of the alarm system, but I'm unsure. It's inside of walk-in closet in the master bathroom.(1)

• The light and fan in the downstairs bathroom

• Light in the garage

• The wall sockets in the living room, only some game consoles, a projector and a soundbar are connected to that

(1) The alarm system looks like it's not functional, but it does say something about smoke detection on the main unit so I'm thinking it might control the sprinkler system as well. We've only been living here since a year and we've never bothered to look at the alarm system since it looks dead.