Your post inspired me to try to fix my silcocks because I too hate that whine.

I looked at the reviews for the vacuum breakers available at Home Depot and, interestingly, I’m not seeing any of the reviews mentioning whine/hum/noise. This leads me to assume that a new vacuum breaker will work fine and that the whine ends up happening when the VB ages (or if you get a defective unit).

, removed the old one using slip joint pliers, cleaned the threads, applied liquid pipe thread sealant, and screwed on the new one.

So far, no noise. Time will tell whether this is a short term solution or if it’ll last a reasonable number of years.

Note that some silcocks will have fine threads for a VB, some not. Make sure you get the right threading for your application.

If your dad already removed the VB then you don’t have this issue, but for others that might stumble on this conversation: Many VBs have a set screw in the side, which is screwed in and then broken off to prevent removal. Code often requires this. If yours is like that, you’ll need to drill out the set screw before you can take off the old one.