2007 XC70: Battery drains overnight, high pitch whine under the hood

[turbo2007]

Are you sure it is #37? That shows on wiring diagram to be MAF and the injectors only. Injectors buzzing would flood engine, maybe even hydrolock it if you attempt cranking. MAF sensor wouldn't make noise.

1st post. Great forum, has helped immensely over the last year.

I have a 2007 XC70, and this sounds like the same problem I am having.
Battery drains overnight and I can here that high pitch whine under the hood. Its very "soft", ie its not a loud noise, just very high pitched. You can barely hear it really. I was going to take a piece of vacuum hose and put one end in my ear and poke around with the other end to see if I can find the source of the whine, but I thought I'd ask first.

Plan B will be to start pulling fuses. I know there's a draw, but I haven't hooked up the Voltmeter yet.
Thought I'd ask and see if this might be a common problem someone knows off the top of their head.

I don't know if this is important or not, but I have a green light around my cup holder that sometimes stays on all night unless I lock the car.

Gremlins... I guess. No water damage anywhere. The car's pristine really.
I put a new motor in it. Got it for $500. 135K miles.

Any idea what this is?

[oragex]

With the engine on, off or ignition on?

[jonesg]

the computer box cooling fan may cycle on and off after shut down by design.
Its located in front of the power steering reservoir.
Circuitry is switched by grounding the neg wire, its always powered up, an exposed grounded wire could turn things on continuously.
That particular 5amp fuse is in the engine bay.

Brake vac pump also makes a quiet hum.

[turbo2007]

the computer box cooling fan may cycle on and off after shut down by design.
Its located in front of the power steering reservoir.
Circuitry is switched by grounding the neg wire, its always powered up, an exposed grounded wire could turn things on continuously.
That particular 5amp fuse is in the engine bay.

Brake vac pump also makes a quiet hum.

With the engine on, off or ignition on?

Engine/Ignition both off.Key out.

I'll figure it out and post back later. Whatever makes that whine, I suspect is normal. I think my problem is elsewhere. Something is draining the battery.

I unhooked the negative battery cable and put the volt/amp meter in between, it read 4.5 amps. But all the interior lights came on too so.... I don't know how much that draw should be.

Something else I'm going to have to read up on, somehow while I was messing with all this (1 AM, freezing with a flashlight) I set off the siren alarm. But the battery was unhooked lol!. When I put the battery cable back on the siren got louder. You guys all probably knew this stuff already, but I guess the alarm has its own back-up battery(?).

Anyway, I'll figure this out like I said. Will post back if I find something that might help someone down the road.

[jonesg]

Yeh, theres a small nicad in the alarm module inside the fender liner, passenger side.
Thats probably due for replacement after 13 yrs too. But not the source of the drain.

Interior lights should go out in a few minutes, close the doors .
Maybe run the outsides the hatch.