Squealing while in reverse?

[MrSam]

Background info: Bought the car 4 months ago, never once have I heard it squeal while in reverse. Went to a friend's home today to have him help me install my new exhaust. Got everything done and went for a drive - asked him to drive so I could record the sound. We got back and he parks my car on his driveway (small hill, not too steep). We both get out to hear the exhaust while idling, then he proceeds to turn off the car (reached in and pushed the key in). Apparently he forgot to put it in park! Car starts rolling downhill, I jump in as it's moving (~5 mph), slam the brakes, and put the car in park - it was in drive.
As I'm leaving his home, I put the car in reverse and hear a faint squeal/squeak, barely audible with the windows up, but clear when they're rolled down. The car only makes this noise when it's reversing, regardless of whether or not the brakes are depressed. Any idea what this could be? I can only assume it was caused by what happened today.

[bluefox280]

With the brakes lightly pressed, there's a sound...
But what if you're hard on the brakes... Does the sound remain?
If not, that's pad squeal which can be remedied by putting anti-squeak compound on the backside of the pads.

Another way to check is lift and the car, place the transmission in Neutral, and rotate the rear wheels backwards.
From there you can isolate the noise (if not pad squeal) and locate the issue.

- Erik

[MrSam]

Thanks, Erik. I just checked, the sound persists even when riding the brakes a tad harder. That said, it's a bit quieter when I brake harder. I'm just concerned that I may have caused some type of serious damage to another component, although it seems unlikely considering the car was moving less than 10 MPH when I had to slam the brakes. Just surprised that it would case this squealing noise.

Also, the noise isn't present when the car is moving forward, regardless of whether or not I'm pressing down on the brakes.

I should also mention that it doesn't sound like your typical "brake squeak." It sounds more like something is loose, if that makes sense.

[bluefox280]

I should also mention that it doesn't sound like your typical "brake squeak." It sounds more like something is loose, if that makes sense.

If so, then time to lift and support the vehicle and inspect to see if there's anything out of whack.
Check pad seating, guide pins, e-brake engagement, etc.

- Erik

[MrSam]

Thanks, Erik! I'm due for a 75k inspection. Just did the oil change, plugs, and filter to reduce the cost. I'll be dropping the car off at the dealership in a few days so I'll ask them to take a look.
This morning I noticed that the car was making a strange hissing sound when changing from park to drive, drive to reverse, etc. I get the feeling that sound has always been there and I'm just now noticing it since I'm actually looking for another sound. Don't know, though.