I know there are a few out there with sound problems in Mail.app relating all the way back to 10.5.0. Mine seem to be getting worse with every 10.5.x update. Mail app now no longer pings when I receive mail however it pings when a new RSS feed is available. It does ping however when I hit send after composing an email. Has anybody found a definitive fix for this because Apple don't seem too bothered about it. For me its a pain in the ass because I can be sitting around waiting for mail that is, unbeknownst to me, already in my inbox thus slowing down my workflow.