tapping noise in 4cyl frontier till it warms up
It could be a slightly sticky valve lifter or it could be a little piston slap. If you want to chase it down, you need to determine if the tapping is at camshaft speed or crankshaft speed. A mechanic with a seasoned ear could judge this. If the noise reliably goes away on warmup, you can ignore it.
If you are in cold weather, this may be a great factor.
For how many seconds and did you use the right oil?