If your expy is making that noise just after having the VCT work done, they likely screwed up the timing when putting it back together. That sound reminds me of an old motorcycle I had when I was young. I rebuilt the engine and it had a similar "tapping" sound but only 1 tap since it was a v-twin sohc. I found out that the timing chain was off by 1 tooth, advancing the cam timing and opening the intake valve much earlier than is safe so as the piston came up to TDC, it "tapped" the intake valve. That is piston-valve contact and is not good. Do not drive it, have it towed. Have them give you a new engine while your at it because they screwed up yours.