Whistle while you (don't) work - odd noises under hood.

Howdy,

I don't come around often, but when I do, I try to pose an unusual question. Search revealed no clues, at least as far as I could find.

Wife's 2008 328i, 37,000 miles, no damage, no other current problems.

When she shuts it down after driving, there is a high-pitched sound, seemingly electronic sounding, emanating from under the hood. It is not continuous, but sounds in several second intervals, punctuated by short silences. It's very high pitched - to the point of hard to tell where it's coming from.

The neighborhood dogs freak out when comes home.

Car runs fine otherwise. Only issue to date - one coil pack died at about 30,000 miles, then one more, at which point the dealership was persuaded to replace the remaining coil packs. Also replaced the battery at five years old when it started to crank slowly.

Any insights?

Your CCV is causing this and it isn't as unusual as you might think.
Its function is to pull a vacuum into a cyclone and separate the oil fume sending the oil back to the sump via a rubber hose to the dip stick and the fumes back into the intake to be burned...
I would think you are getting a partially plugged CCV. They don't usually clean out well and are fairly cheap.
Try this remove the plastic hose to the CCV while the engine is running. It will run a little rough but will be OK. Now have her shut the engine off and see if you still have the sound. The only other location that makes sense is the vacuum booster releasing its vacuum back into the engine. There is a check valve for this which has been known to lead too.
My best guesses...

Great insights, thanks.

I will check this out and post results.