Visual and audible alerts not right

Default Check Interval = Globally

Check interval = Individually account/host

My setting and never touch on Globally set at 10 minutes as before,
while I adjust on Individually account/host to 1 to 3 minute.

I believe, the 'Default Check Interval' is merely a number used to set intervals for accounts as you define them so you don't have to manually specify an interval (enter a number in a box) for each definition. And, initially upon X-Notifier installation, 10 is the suggested interval.
- Checking more often than 10 minutes is sometimes referred to as 'hammering the server'... Microsoft servers will complain if you check more often than about 15 minutes.

The developer allowed for changing the definition default with the 'Default Check Interval'... so every time you define a new account, the definitions start with this 'global' default (as CFBancroft suggests)... but this default does not 'globally' tell X-Notifier how often to check... accounts are checked by each individual account's setting.  The account setting is the check activator... the 'Default' is for defining new accounts (saving you some keystrokes).