Mysterious "flushing toilet" sound from rear of Toyota Sienna



I wish there were some other way to describe the noise that’s coming from the right rear of my 1998 Toyota Sienna - but there’s just not! When I brake fairly hard, I hear an unmistakeable sound of rushing water - almost exactly like the sound of a flushing toilet when you are in the next room or downstairs. My kids noticed it first since they ride in the back seat, but I honestly didn’t believe them until I drove the car today by myself and heard it too. I’m hoping that someone can at least give me some hint as to what it might be so that I can call my mechanic with a straight face. I’ve checked all obvious things - no liquids in the car, no toilet either, and nothing’s leaking from underneath. Help please!!


My best guess is that there is a drain plugged someplace and some rainwater is trapped in the body (i.e., inside a door, wheel-well, etc.). I would put it on a lift and try clearing out all the various body drains. Leaving water trapped can cause rust.


It could be antilock brakes working.


I agree. There is definitely some water trapped somewhere within the vehicle’s body, and it’s sloshing around when you turn or brake. It could be trapped in the fenders, liftgate, or under the rear floor.

Putting the vehicle on a lift and making sure all of the body drain holes are clear is probably the best way to deal with this.


You’re absolutely sure you’re not hearing gasoline sloshing around in the gas tank?


Don’t forget the drains under the doors.

  • mountainbike


An idea – It might be a problem with the brake on the right rear. Metal to metal contact can sound like a rushing sound. So have someone rule out a problem with the brake on that wheel.


The mysterious sound was identified by my local Toyota mechanic in less than 5 minutes, and it was indeed a large amount of water sloshing around in the rear - just as it sounded! But, luckily, no harm was done. Unbeknownst to me, there is a plastic tank to catch condensation from the rear a.c., located in the right rear of the car. It had become clogged somehow and was full of water, which caused the sloshing sound I heard when I applied brakes or turned the corner. Thanks to all for their suggestions - I’m so glad it wasn’t water trapped in the body of the car or in the doors.


I’m glad your car is fixed. Thanks for coming back with feedback ---- so many people don’t. Feedback helps to show when I/we am/are right, which helps me/us to give even better advice.