BlackBerry Curve has an option to turn off clicking sound generated for Trackpad. The setting to mute the click sound is available as part of the BlackBerry Options.
Press menu button and select options from the settings list.
In the Options screen navigate to Screen/Keyboard options
In the Screen/Keyboard. scroll down to Trackpad section.
Set the drop down value for Audible Roll from Click to Mute.
If you are prompted with following Changes made screen, the select Save option to confirm the changes.
By this way we can turn off the Audible Roll for Trackpad in BlackBerry Curve 8520 Smartphone.