Do you get such kind of sound every time you use the above mentioned key combination?
Could you please check this issue with a new catalog?
Yes when I add the Alt key to the minus or plus keys after selecting a slider to adjust the bell rings each time I enter Alt-minus or Alt-plus. I'm not sure what you mean by checking with a new catalog; do you mean create a new catalog, enter some images and see if the same behavior results?
Exactly, please create a new catalog and check if the issue persist there or not.
The problem still exist in a new catalog.
Please try to rest Lightroom prefernces by holding the Shift + Alt key while launchig Lightroom and check if the issue persists or not.
I can confirm this happens to me as well using LR CC 2015.3 on Windows 10.
This seems to be a bug. Alt and something causes a warning sound. It's not the catalog or the preferences, LR has a UI issue, at least on Windows.
Turning off your speakers or setting the system volume to 0 seems to be the only way to keep from hearing the sound.
Able to replicate it on my PC:
The beep plays as the ALT + "-" , ALT + "=" and ALT + "+" etc. keys are invalid Lightroom key combinations within Windows??
I see that on the LR6/CC Keyboard shortcut list that the "Move slider value by smaller increment" shortcut is shown as "blank/none" for Windows PCs but on a Mac you can use the Opt key.
However, I found that using Lightroom CC2015.3 the ALT keyboard shortcuts for "Move slider value by smaller increments" do work but with the beep.
Though in either LR 5.71 or LR4.4 the ALT key combinations do not work for the smaller increment adjustments and you just get the beep.
Workaround: You can disable/set the Windows default beep sound to 'none' under "Sounds" in the Windows control panel.
FYI: In case anyone asks it is not the same a "Sticky keys or "Toogle keys" beep.
bhousto90 is correct; according to the latest Lightroom CC manual the use of the "Alt" key in combination with the plus or minus key is not listed for either Windows or Mac. I should have checked first. Thanks to all for the help.
FYI they to way to get smaller increments is explained by Laura Shoe; first click on the numerical value for the slider in question and then use the up and down keys to adjust in small increments hitting enter when finished, for the saturation slider I was working with this reduced the increment to 1 from the default value of 5 when using the plus/minus keys.