Anybody know what's causing this sound?

Probably the accumulator and pump assembly I don't know if you intended to post a sound bite it didn't post

 

If you stand in front of the car and look at the silver thing that says hybrid synergy drive the inverter right behind it and slightly to the left on a bracket is this big thing called the break actuator accumulator It's the brake pump part of the business It's not the part that your foot deals with that thing clicks makes a racket so on and so forth especially from 150,000 mi on up or somewhere in there or say after 9 years if we're dealing with just time it is time sensitive as well as wear sensitive these electronic parts that is so today these 0809s '07s they're all well over 10 years old so any of these medium wear electronic items like the brake pump are subject to be getting flaky it's just the nature of the electronic part I guess but then again some slip through I've seen some at 430,000 mi with the original brake pump and the original hybrid battery working in operating seemingly fine I don't get a chance to take those vehicles into the mountains and see how bad they'll do I just get to work on them and send them on their way we're pretty much in the flatlands here so we can get away with seemingly quite a bit.

 

the brake actuator sounds when you open the drivers door. it's more of a buzzing to me, and sounds like it is under the hood behind the dash, which is where it is.

a ticking from under what seat? the battery is behind the rear seat

 

Yellowjackets!

Personally, I would try to repo sound as I lied under the car or across the back seat or woth head underhood to narrow down.

And you have posted this in two separate places. Highly frowned upon

 

How is the 12v health?

 

It might be broken, idk.
Can you upload a video?

 

Did you try a thumbnail? I don’t think I’ve ever uploaded a video.. some people place them elsewhere, and provide a link

 

i have never heard of anything like it. it sounds like someone is tapping on the board. can you remove it?
otherwise, maybe get under it or a lift to see if something underneath is rattling

 

does it stop when the engine shuts down?

 

Put me down for a brake system issue. A strong hint is the starting when you just get in the car, because that's when the brake pressure pump will start to run (triggered by opening the driver's door) in preparation for driving. In the background of the recording, faintly, I do think I hear a constant buzz that reminds me of what the pump sounds like. The engine isn't running at this point, right?

If there is some leakage around a hydraulic valve in the brake actuator, the pressure being built up by the pump could be leaking into one of the rear brake lines, giving a fluctuating pressure in that line and wiggling the components at one of the rear brakes. I'm purely speculating here; a mechanics' stethoscope (they're cheap) would tell you if I'm on to something or not.