Abnormal "water" noise during braking/acceleration

[flyingprius]

Recently my Prius has been making an odd noise as if water were being spashed around below my rear passenger seat. I notice the noise during moderate braking or braking and subsequent hard acceleration. I am wondering if there is a possibility of it being fuel splashing around....? My 2004 Prius was manufactured September 2003 and it has 18300 miles... If anyone has any ideas or similar experiences, I would appreciate hearing about it.
Cheers,
Flyingprius

[KTPhil]

I would check that the package tray (under the rear compartment floor) isn't holding water. Maybe a leak or spill put liquid into it. It's the low point of the rear interior of the car.

[flyingprius]

Thanks for the suggestion, I looked there and I didn't find any water. I am still curious as to whether or not it's a fuel issue. The fuel door is on the driver side, so is the fuel tank on the driver side? My rear passengers say the noise is coming from the passenger side. It's not particularly bothersome, I'm just worried it may be an indication of something serious. I have no annunciator lights, and I get 48 mpg in rough driving, so I don't think it's totally pressing...
I just don't want my Prius sitting around at "southern comfort" Toyota for a week while they go tearing up the back of my car.
Any thoughts are appreciated.
Flyingprius

[nevesis]

I have experienced the same sloshing noises you described. The first time I heard it, I was quite perplexed. However, I figured it was just the fuel in the gas tank. Since the car is so quiet, you can hear just about anything else going on, and that fuel is prone to moving around in there, even with the bladder. In fact, the bladder is probably making it more noticeable, as it gives the liquid more to move around.

I can't say for sure, but I would place my bets on it being the gas tank. But I get it too, and my trunk is not full of water either, and I didn't leave a gallon of milk in the back seat from last month. heh.. I haven't even noticed it lately, so perhaps it is intermittent (maybe the bladder did not inflate during a particular tank drain cycle?)

Personally, I'm not too worried about it. I'd rather have a nice soothing slosh slosh sound, along with the whir of the electrical drive then a putter of a gas or diesel engine.

[KTPhil]

Perhaps the sound of gas sloshing is noticable on the passenger side because the air vent on that side leading to the battery (near the tank) conducts sound.

[Prius Maximus]

I also have the sloshing noise. To me it sounds like it's coming from the engine compartment. It's hard to tell though, because sound travels in a car, and I rarely have a passenger to help me listen. It's only noticeable when accelerating or stopping, and occasionally when turning.

I haven't noticed it being more or less common with a full/empty gas tank.

[thomastz]

I am getting the sloshing noise on stop and go situations also. Has anyone figured this out yet?

[David Beale]

Did you look -under- the package tray under the spare tire? If not there then it's time to walk around the car with a screwdriver. Under the side sills look for water drain slots. Use the screwdriver to ensure they are clean. Do the same for the rear lower fender, behind the rear wheels. There is one other place you can accumulate "crud" (technical term ). You have to remove the wiper arms, then the plastic cowl cover to see the drain holes for the cabin air intakes. Leaves etc. can plug these holes and water can pool there. There are detailed instructions with pictures on this site for this service - see mouseproofing your Prius.