I have an '02 Passat wagon, 1.8T and AT.
A few weeks ago I noticed a muted "tic-toc" sound coming from behind the dash, repeating at an interval of about 5 seconds or so.
I noticed it first on driving down the alley and navigating the local streets. After a few minutes and on the freeway, I'd only hear the sound when the engine was under load, not when coasting or idling at a stop. After about 20 minutes or so, it would stop altogether, although on longer drives it will start up again for a few minutes and stop again.
There are no starting or driveability issues and gas mileage is as expected for the temperature.
Any idea what I'm hearing?