Nokia N8 Forums show the Symbian device is making strange chiming sounds even though no alerts have been enabled. Sometimes the user has set that if a message arrives, only then a noise occurs or a noise only occurs during a specific cause.
There may be another problem which surrounds the email settings, perhaps when the user was setting the desired configurations – a mistake may have happened. If the cause may be that the email notifications are making a noise then have a look at the Sync frequency, set it to manual to eliminate the problem.
Or you could have a look at the profile settings of all the profiles rather than just one, just to be sure of any misconfiguration. Depending on the noise, the options may vary. Proceed to the main menu, settings, profiles, check all the profiles or the desired profiles.