Prius changes its own volume

I have a 2006 Prius that periodically changes its own volume. The volume goes up and down, and I have no steps to reproduce the problem. I’ve had the car in to the dealer three times and they haven’t been able to reproduce the problem and have no ideas, and I’ve also talked to Toyota ? no ideas there, either. Has anyone else encountered this problem? Any solutions?

The speakers don’t change volume on their own; they do not supply power. It has to be the car stereo. Replace it. You might find a used radio for an attractive price.

It’s under warranty, so Toyota will replace it if I can prove it’s the stereo, but I have to prove it. And because the stereo includes all climate and navigation controls, it’s an expensive proposition to replace it on my own.

This is probably a feature on the radio that increases the volume to compensate for noise from the engine, the road, and the wind. Check out a Prius forum to find out how to disable this feature.

Lots of cars have automatic volume control that boosts the level depending on the speed of the car. You can usually modify or turn this off. Look in the manual for AVC.

This does sound like automatic volume control. If you’re not used to it, it can seem very strange. I once drove a Chevy Impala with that feature, and hitting a pothole would cause the volume to increase A LOT, for about two seconds! Check your owner’s manual to see if there’s a way to disable it if it bothers you.

Automatic volume control is turned off. Both the dealer and I have verified that several times.