Im not sure if this website best place to ask, but my mom recently got a 2008 Toyota Highlander Hybrid but we notice every time she hits brakes before turning on the car. We hear little knocking noise, kind of sounds like your drinking something. I thought it might be weird battery/engine doing something to make car start and maybe it’s normal. The car also scans the car when turning it on and stated everything is fine. But I want make sure if anybody experienced this problem or feel like we should get it checked out? What do you guys think?
My guess is that it’s part of the car going through its normal startup routine. You might find a Highlander hybrid forum and ask there, too.
It sounds to me like you are hearing the electric brake booster. Traditional car engines use vacuum from the engine to boost the brakes, but on a hybrid that does not work when the engine is off. Instead, an electric pump is used.
If you open the hood, and stand in front of it (with the engine off) while someone repeatedly presses and releases the brake pedal, you will be able to hear exactly where the sound is coming from, and it should be the brake booster pump.
(Note: this is based on my 2017 Highlander Hybrid and a friend’s second generation Prius. Since the 2008 Highlander hybrid falls between those two vehicles, I see no reason that it should be any different.)
Is it something I should be worried about?
If it is what I think it is, it is perfectly normal behavior for this vehicle and nothing to worry about.
Of course, it is also possible that it could be something else entirely, so if you have any concern having a mechanic listen to it is probably not a bad idea. A mechanic who specializes in Toyota hybrids might even be able to listen to it over the phone.
Alright, thank you