Troubleshooting: Random letters appearing while typing on your iMac M4
Thanks for the detailed description. The fact that random letters such as "y" and "r" appear while you're typing, and that this happens in virtually every application, is an important clue.
Since the problem started after upgrading from macOS Golden Gate 27.1 to 27.2, it's possible that a software-related issue is responsible. However, we should also rule out a keyboard problem or an application interfering with keyboard input.
I'd suggest trying the following steps in order.
1. Save your work and restart your iMac. Then test your keyboard in Notes, Word and an email application.
This is a simple first step that can sometimes clear temporary system or keyboard-input problems.
2. If you're using Apple's Magic Keyboard:
- Check its battery level.
- Turn it off for 15 seconds, then turn it back on.
- If possible, connect it directly to your iMac using its charging cable and test again.
If you have another keyboard available, try that as well.
Why this matters: If the problem disappears with another keyboard, the original keyboard or its Bluetooth connection may be responsible. If it continues, a software issue becomes more likely.
Apple's guide: Connect a wireless keyboard.
3. Go to System Settings >> Keyboard and check your input source, text replacements and key-repeat settings.
Next, go to System Settings >> Accessibility >> Keyboard and make sure Sticky Keys and Slow Keys are turned off unless you use them.
Also check System Settings >> General >> Login Items & Extensions. Temporarily quit or disable nonessential third-party utilities, particularly text expanders, clipboard managers and keyboard customization applications.
Apple guides:
4. This is one of the most useful diagnostic tests because it helps identify whether a background application or extension is causing the problem.
On your M4 iMac:
- Shut down completely.
- Press and hold the power button until startup options appear.
- Select your startup disk.
- Hold down Shift and click Continue in Safe Mode.
- Open Notes and try typing for several minutes.
What the results mean:
- If the random letters disappear, a third-party application or background process may be responsible.
- If they continue appearing, a macOS-level issue or keyboard hardware problem becomes more likely.
Restart normally to exit Safe Mode.
Apple's instructions: Start your Mac in Safe Mode.
5. Since the problem appeared after installing 27.2, check whether Apple has released a subsequent update.
Go to Apple menu >> System Settings >> General >> Software Update.
If an update is available, make sure you have a current backup before installing it.
Apple's instructions: How to update macOS.
It's possible that this is a software bug introduced in 27.2, although we don't yet have enough evidence to confirm that.
6. As a final diagnostic test, try creating a temporary Standard user account under System Settings >> Users & Groups >> Add User.
Log into that account and test your typing.
If the problem disappears, something associated with your normal user account may be responsible. If it continues, a system-wide issue or hardware problem becomes more likely.
If none of these steps helps, contact Apple Support and explain that the problem began immediately after the macOS update.
My recommendation: Start by testing another keyboard, if available, and then try Safe Mode. These two tests should help determine whether we're dealing with a keyboard problem or something introduced by the macOS update.
