servicing? If more than a day or two -- not unusual to get that tapping (happened to me and others have posted about it too). Issue is oil draining down from the block/CAMs.
Took a good 20-25 minutes of idling for it to get a lot better (had me really worried at the time too). For me it was coming from the driver side intake/exhaust valve cover area...
If you think it's the t-belt slapping the timing cover - can also remove the driver side cover for an engine running inspection?