I have a single-tap or knock sort of noise at startup after my car has been sitting for a day or two. It just started within the last couple of weeks. The best way I can describe it is someone holding a drums stick and hitting a desk or something. It's just the one single thap/knock noise, and then it's never heard again until after the car sits for a day or two.

Could it be the starter? I kind of wanted to get some ideas before taking it to my mechanic. I trust him, but I also don't want to tempt him to rip me off lol.

Without hearing the sound, it could be the purge (gas vapor) valve. It can make a "heavy" ticking sound. It to will generally go away once driving, until it gets really bad.

Thanks for the reply. It's not a ticking sound, just single thap/knock sound. Based on some general searching on Google, it doesn't seem like it's anything of immediate concern. I'll just bring it up to my mechanic next time I'm in.

I don't know that engine (sadly), but, if it has hydraulic lifters, what comes to mind is a single lifter that loses its oil after sitting still for a long time. On the next startup, it would do one or more ticking or knocking noises until the oil pressure is restored within the lifter.

If it's that, it's usually not a major concern.

IT could be something else that relies on oil pressure, and takes a long time to drain.