Odd screeching lock sound suddenly with iOS 4

I was having this problem and turned off lock sounds then turned them on again and the problem seems to have gone away now (fingers crossed!).

same problem

http://www.youtube.com/watch?v=KKYUGrlgxcU

Mine sounds the exact same as the you tube video. Is it iPhone 4 or just the new OS?

Same problem on a 3GS with iOS 4. How odd.

http://vimeo.com/12883270

I had the same issue once so far. It happened a couple of times in a row. I attributed it to an app running the in the background and eventually quit all the apps and it went away. It was strange, like a feedback loop or something. It hasn't happened again.

Count me in as a victim of the screeching cricket. As noted by others, fortunately it doesn't last more than a couple of seconds.

After about a week of observation, I note that it seems to happen when I press the lock button AND have an audio-heavy app (e.g., NPR Music or Pandora) running in the background or "dormant."

Ditto. Mine usually make the screech after I get a text or email message, either in place of just after the actual chime.

Once it happened while listening to a song in the iPod. It played it for just a half second as one track was ending and another beginning.

Im having the same problem when I shut the phone off, No clicking sound anymore, After I reboot the phone, it will work for a little while then stop again. I Restored the phone and Im having the same problem. So don't restore, It wont help and its a hassle.. Help !

I had this issue with my iPhone 4, but it had been intermittent. I called Apple Care last night and found out it was because the app, Recorder by Retronyms was sending sound waves that were going through the microphone. I did a restore as new and, so far, it's fixed. If it keeps happening, I'll delete the recording app.

Yes. This also happened to me, and just as mysteriously it stopped.
So far the issue has not repeated.

OMG this same thing just happened to me like 10 minutes ago. Ok picture this... It's 12:15am I'm in my bedroom in the dark getting ready to go to bed. I push the screen lock button and all of a sudden that evil screeching sound started. I swear it all most scared the **** out of me. Keep in mind I live all alone in a huge house here in Jordan (Middle East). Im already on edge here. APPLE please fix this issue ASAP. I'm using an iPhone 3GS running iOS4 4.0.1.

This happened to me after upgrading the 3Gs to iOS 4.0.1. I have restored the phone back to original and installed 4.0.2 and it is still happening. Reboot doesn't fix it as it comes back eventually. Turning the lock sound as others have suggested fixes the screeching after unlocking the iPhone but if you have system sounds enabled for email, texts, etc, it will screech too when those sounds are generated.

I had to turn off those sounds to be able to get it to stop. If the phone is on vibrate mode this won't happen at all. Seems like to me like the mics are being opened every time a system sound is generated, creating the feedback. It feel, sounds and smells like a bug. A pretty annoying one to say the least.

I guess if I need to keep rebooting my phone to fix the issue I might as well switch back to my Windows Mobile phone. 😉

Apple, please stop dropping the ball with crappy updates and get your stuff together. Fix this.