Strange 'glug' sound from supply behind the wall - new plumbing
About 3 weeks ago I had a tile shower put in, and the plumbing was all new (off of the original supply lines anyway). The guy used PEX from the copper lines up to the valve, then PEX again from the valve to the showerhead. The bathroom isn't quite done yet, so the shower hasn't been turned on yet. Tonight I started hearing this very regular 'glug' type of sound behind the wall.
It's sort of a faint click or pop, but there is a noise about every 3 seconds for a little while, then it stops. Comes back again about every 10 minutes. I'm panicking now because the tile is obviously very permanent, and the backside of that wall is up against another recently re-done bathroom (base cabinet and medicine cabinet are directly behind this plumbing wall).
I took the escutcheon plate off the shower valve and flipped my flashlight around. I noticed that when I hear the noise, I can see the water through the PEX that goes from the copper supply to the valve bouncing up and down right before it gets to an elbow. There is an air bubble between the elbow and the valve. I don't see anything dripping around the valve at all.
Is this noise something to be worried about or is it just the water pressure putting an occasional squeeze on the air bubble? Does what I'm saying even make sense?
Ugh, please just tell me it's fine, and I don't have a slow leak 2 feet from hardwood floors.