I eventually did decide to return my Garmin (again) due to the lack of sound. Three days after I dropped it off at their office in Totton (I’m not sure what the security guard thought of me as I was wearing running kit at the time!) a package arrived back. Sadly this time it just contained a watch, not a whole replacement box. The wrapper stated “Newly Overhauled” but the watch has a new serial number so I’m not sure what to make out of that. I can, however, do intervals once again without having to look at my watch the whole time!