"Pop" noise driver side
 

Hey guys,

So when I enter the car and put one foot in the middle of the driver's floor side, I can hear a "pop" under the carpet, like when you push the metal body of a door (for example) and you see and hear the "pop" and a temporary dip, but when you stop the pressure, it comes back to its normal condition with another "pop" sound.

Visually, there are no stain on the carpet and nothing "weird" under the car that shows something was "repaired". Wanted to check with you if this is normal.

Thanks.

pull the carpet back and look. Can't say i've ever had the happen on either of my cobalts or anyone's cobalt I know

^me either. Floor is pretty strong. Has it been in an accident?

Here are some pictures of what's under the carpet.
Notes:
- The driver side and passenger side are very similar.
- There are no signs of anything work done under the car: no soldering, no "weird" parts, fixing, anything. Just pure original metal - at least from what I saw. Both sides are identical.
- The carpet and the floor are wet. I'm letting it dry for now.

This is under the carpet from driver side:
Attachment 62965

This is the passenger side:
Attachment 62966

I was trying to find where the "pop" sound was coming, and then some of the "stripping" stuff came out. The dark region is where the pop sound occurs. The region in front of the rust, when pressing it, creates a dip (max 2-3 mm) and the pop sound. When releasing, it comes back to the original form.
I must say, this does not seem to be a "cut". You can see there is a rectangular pattern which gives the idea that there are some non original work on that. But the passenger side has the exact same spot.
Attachment 62967

There is absolutely nothing suspicious under the car at this exact spot. No hole, rust nothing. So I believe this came from inside the car. Maybe from the previous owner, who knows.
The question now is how to repair this.
Any ideias?

Thanks a lot guys.

Sounds like it's rusting in the floorpan. I'd start to clean the area and strip it down to bare metal. Remove all rust and scale buildup, then paint or otherwise seal the metal and add a layer of sound deadening material to replace the glue that's there from factory.

Find the source of the water though, that area should always be dry. If you keep getting it wet it will eventually rust through.

Thanks Joe.
I am doing an investigation from where this water may be coming from, but without success until now.
The sunroof drain tube (which I read is to be a common cause of water on the driver side) is not clogged. It ends on the A pillar right below the lever to open the hood.
This yellow foam (that I can't remember the name now, I think is something related to fire deterrent) is also soaked, but only near the edges and in the middle.
I hosed all the front and roof of the car for several minutes to see if I could find a leakage, but nothing. I only see humidity. Will have to dry real hard before trying again.

You could have a plugged evap drain, to where the blower housing fills up with water and leaks into the interior. Quite common. Try running the car closed up with the a/c on high for a while and see if there's a good stream of water under the car and no water on the inside floor/console areas.