Sonic Grenade is a free app for S40 that plays a high-pitched noise through your device.
The interface takes the form of a picture of a hand grenade which you tap to start playing the noise. There are two pitch settings to choose from, both of which are highly irritating. The app is designed for playing pranks on people, but you should be careful with the volume if played through an amplifier as it could damage hearing. Sonic Grenade lacks any other options other than the two pitch settings.