Odd, slow speed sound

[Siggy]

Recently changed the oil and filter, along with the front brake pads on my '12 3.0 gas engine.

A few days later, I was sitting at a stoplight and heard a faint noise and I thought it was the car next to me. Didn't pay much attention until the next light, when I heard it without the other car there.

It's a very very faint noise, imagine someone taking the handle end of a screwdriver and tapping under the front left of the car just hard enough to barely create a sound. If the radio was on, you wouldn't hear it.

The sound happens about every 3-4 seconds. Racing the motor doesn't change the tempo. It's just a steady, every 3-4 seconds, very faint "knock". Kind of hollow sound, that's why I said it sounds like the handle end of a screwdriver hitting something. You can only hear it when sitting still. It might be happening when moving, but you can't hear it.

Only thing done is the brake pads and the oil and filter. Everything seemed normal during those changes, nothing jumped out at me.

[andrewwynn]

What's the ambient temperature and what is your heater temp set to?

Also could you almost describe the sound as a "heart beat" (it can be a double tap. Dup dup).

If so, I have a solid guess of the source of the sound:.

Water valves for the heater cores.

You can easily confirm by open the hood and hold a gloved hand on the heater valves: just in front of where your right knee is if you have left hand drive. Close to the firewall. (that's on my 3.0; might be slightly different if v8 motor. )

Drove me nuts for months until one day I was poking though real-time data on my foxwell and had the valve status open and the left/right valves were opening/closing about every 3-5 seconds slightly offset from each other in perfect sync with the odd tapping sound.

If you have a scanner that will display real-time data that's even better way to confirm.

Your description exactly matches my experience with the heater valves though so I'm willing to put 90/95% odds.

[Siggy]

Good question, ambient temps in the 40-60 degree range, heater set to 70-72. I haven't noticed a double tap, just a single but I'll focus on it a little more now that I've posted it.

So it would be normal, if it's the heater valve?

[andrewwynn]

Very normal and that's exactly the ambient/set temps I would expect to hear the "heartbeat".

You might have one valve slightly louder than the other so you don't hear the double beat.