A couple weeks ago I noticed that my 13 G37 Sedan would make an odd water sloshing noise. The only times I ever hear it were when it had been stationary for at least 15 seconds and then I accelerated. I was able to hear it in reverse as well. It seems the actual movement of the car is causing the sound and not the revving, as if the car remains in park, the noise is not audible. Took it to a mechanic and they had "trouble replicating the noise" and checked the a/c drain and the sunroof drain - said both were fine. When I mentioned possibly air in the coolant, which the level is fine and has been slightly above max the last few weeks I've been watching and it's not moved at all, they claimed to think the noise would be more frequent and that they tried shaking the car and it wasn't making any noises. Below is a video but it's hard to capture the sound (easier to hear with headphones on). It's about halfway in where I take off in drive after backing out of the driveway. I hear it most prominently in the driver's side dash.


Anybody have a similar type of noise, before? Car runs great, a/c blows frigid cold and heater blows fine. I replaced the battery about 4 months ago - could water be getting under the cowl if I didn't put it back on correctly? I don't see any sign of water anywhere in this car or in the engine bay.

 

No video, but experienced something similar on an older car when cooling system was improperly bled. How long you had the car for? Any cooling system work recently?

Can you reproduce on demand?

Note, deleted your duplicate post. If you need to make changes, you can always edit.

 

For some reason it won't let me attach the video from my phone on either the desktop or mobile site. I'm working on getting it on youtube and will update with a link.

I've had the car for 4 years and the coolant was replaced about 1.5 years ago at somewhere around 50k miles. It now has 73k miles. I normally don't have my cabin this quiet, but a couple weeks ago I was driving an inlaw somewhere and didn't have the stereo on and it was the first time I noticed it. No cooling work done since then, though I did change the serpentine belt which required my to take the overflow reservoir off and put it back on. I changed the spark plugs, cleaned the MAF sensors/TBs and replaced the brakes a few months ago along with the battery swap mentioned.

I can pretty much get it to reappear on demand by just stopping the car (like at a stop light) and waiting for about 15 seconds before moving. It just sounds like someone flushed a toilet. Only lasts for 1-2 seconds. I specifically took it to the place that did the coolant flush 1.5 years ago assuming they would notice it and just burp it for free, but they claim only 1 person "maybe" heard it and that they didn't think it was cooling related given that it only happens under the particular circumstances.

 

My neighbors Altima had a similar, "water sloshing" issue.

Try swinging each door back and forth a few times and see if you hear water. This was a semi-notorious problem on some Altimas and Maximas where the weep holes at the bottom of each door would become clogged with dirt/debris. The doors have small holes at the bottom, usually behind the rubber welt/seal, that allows rain water to drain out.

In my neighbors case it was the rear, passenger door that had close to a gallon of water in it.

Worth checking...?

 

I also changed the cabin air filter about a month ago after I noticed a musty smell when I first turned the a/c on. It didn't really help, but the smell is only there for 1-2 seconds before it goes away.

 

This morning - car off for 16 hours

Last night - car off for 8 hours
I checked the coolant level at the radiator cap last night before leaving work and it looked low. I could see it all the way at the bottom, just a very small pool - but shouldn't it be filled up to the top? Like the level doesn't even reach the large hose that connects right there. The overflow tank is above max by about a 1/4 inch - 1/2 inch so I'm wondering if there's something preventing the coolant from getting sucked back in when it cools down. When I checked this morning it was bone dry inside.

 

Maybe you have a leak, pinched hose, or radiator cap isn't working right. As it cools, a vacuum is created which is supposed to suck fluid in from the reservoir.

Level in radiator should be right at the top.

All I hear in your video is your exhaust noise.

 

Edit; Derp didn't read. Was gonna say sunroof drain, couldn't hurt to check the floors.

 

So I took it to the dealer today - they say there's a very small head gasket leak causing exhaust gases to enter the cooling system. When they were trying to burp the system they noticed that every so often there would be a slight misfire and then gas bubbles would come up. Has anybody tried any of these "stop leak" tabs/fluids? They said they wouldn't advise doing anything since it's so small, but that over time it would cause the same noise issues and loss of coolant being displaced by gas. I'm wondering if anybody's had success with those tabs you put in that are supposed to plug small leaks?

 

They also noted that the root cause was the throttle bodies? PSI in the chambers is too high. Does that make any sense? I did clean the TBs a few months ago but I don't see how the throttle bodies have anything to do with combustion gases getting into the cooling system. Would it make sense to replace the gaskets and ensure proper torque when putting the TBs back on? I honestly didn't bother with torquing them back on as I only had a 1/2 inch torque and it wouldn't go that low.

I did check the coolant level after it cooled down when i got it back from the dealer and it was full, even splattered out a bit when I released the pressure on the cap. I am still hearing that sound though when accelerating so it's possible the cooling system issue isn't even related.

 

Better to replace gasket then use those chemical sealants

 

So I've monitored it over the last week since the dealership drained and refilled along with a new cap. The sound is still there from time to time. The level in the overflow seems to remain pretty much constant, while the level in the actual radiator slightly drops every day. The longer I wait to check, the lower it seems to get. i.e. if I check it 2 hours after shut off the cap will release a ton of pressure and the coolant level full, but if I check it 12 hours after it'll only release a small amount of pressure and be lower in the radiator than full (but still visible). If I squeeze the upper radiator hose while cold I can hear the coolant move, so it isn't fully filled when cold. Every day/other day I would take some coolant and refill the radiator to the top, but it still continues to get slightly lower. Is this normal? Or should it be at the top all the time, no matter the condition? It even lowered slightly between when I refilled it to the top at night and when I checked in the morning - though the engine was slightly warm but I don't think enough for coolant to expand. There has to be some kind of leak somewhere, right?

 

I really hate to even suggest it, but these symptoms sound like a head gasket. I had a Mercury Montana that did the same thing: losing coolant, but there was no white smoke or milky oil.I tried "burping" the system 20 times, but kept losing fluid and making gurgling sounds. So I finally bought a combustion leak detector kit, the ones where it tests for combustion gases in your radiator and the fluid turns from blue to yellow. And I finally had found my problem. Something to search into and possibly try, takes 5 mins.

Edit: Sorry, just read a couple posts up. Guess you already knew that. My bad, it's time for bed...

 

Squishy rad hose is time to replace it

 

Any head gasket leak is worth replacing! ASAP
I wouldn't recommend those radiator tablets.

But I always go for the simple/cheaper fixes first.

Your radiator cap behavior reads as odd. Replace it

Some people will forget to run the heater while burping. Trapped air in the heater core never gets a chance to circulate and escape. Run it with the windows open

Have you considered eliminating the coolant lines to your TBs? The oli filter warmer?
It's your call, consider your climate...

Good luck!