Normal for brakes to make squeak/hiccup if pressed deeply and released?

If something metal hit the bottom of my car loudly I would take a look under the car for damage. Do you know the general area of the hit? It may be worth putting it on a lift for a full undercarriage inspection and while its up there have the transmission fluid changed too since this is a fairly old car and new to you.
I always change all the fluids on any used car I buy no matter how they look. I recommend changing the Inverter coolant also. Many how too's here and lots of You Tubes on that too as its a fairly easy DIY.

As far as the brakes once in a while when you press the brakes it engages a small motor up front that creates vacuum for the brakes. This motor when running makes a faint tickity tickity noise for a few seconds while it runs. It only runs for a few seconds then shuts off.
If you have good hearing you'll hear it all the time.

You can make this brake vacuum motor run by sitting at a light with engine off and press the brakes firmly a few times and then listen.
Hopefully thats it. If thats not the noise get the car up in the air and find out what it hit asap.

 

Have you found anything out about this? I'm noticing it on my '08 Prius. It sounds like a weird burp, almost like someone's tapping a low-pitched car horn.

 

This is a well known Prius problem. It is caused by a small amount of air in the brake system. It often gets worse with altitude, however it is not dangerous. It can usually be cured by bleeding the brakes. There is a Toyota service bulletin out for this, see below. Also much information in this link. Do not attempt to bleed the brakes yourself unless you have studied the many posts here on the subject. It is not the same as bleeding normal car brakes, and will likely end up with an expensive trip to the dealers.
My Brakes are Barking at Me

T-SB-0307-08.pdf

John (Britprius)

 

Thanks John! I'm consoled by the long the five-page thread detailing the same thing. I got my Prius used and it makes interesting noises that this former combustion-only driver isn't used to.