Ticking under the hood

So I'm at the pump filling up mom's car tonight and hear a ticking. I've heard it before, but I finally decided to investigate. It sounds like a relay clicking, but very very fast, like 2 or 3 clicks per second. I revved it a little bit, and it remained there. I revved it a lot, and it went away probably around 2500rpm. Sometimes when it went back to idling it wasnt there until I would just barely touch the throttle...sometimes it came back on it's own.
I pinpointed it to a little plug by the air box. It's a gold unit with a blue plug hooked into it. I could feel the ticking. Anyone know what this is, and why it's soo annoying?

i have a 03 matrix and it does the same exact thing. its located under a black box for me under the hood. id like a answer also

You didn't say what year and engine, so it's hard to know what you "see" and hear-- injectors make noise that coincides with RPM, some engines also have a cold start injector that will only operate during warm up -- injectors have electrical and fuel inputs, so they should be easy to ID.

Generally, relays should not be "ticking" very rapidly -- sure it's not the turn signal/hazard flasher? They make noise on purpose, but they're usually in the interior, but they may also operate a relay under the hood.

Lastly -- some engines have a MAF [Mass AirFlow] sensor (in the intake tract) that heats a fine wire using battery current, resistance is measured across this wire to determine airflow -- there may be a relay here that is intentionally intermittent so that the wire does not burn, and so that resistance can be read on intervals(?).

thats true but i hear mine around where my intake is. so whatever is around it, its making a ticking noise but thats only when the car is warmed up and the oil temp is warm.

Have you recently checked the amount of oil you have in your vehicle. Believe it or not I had a costumer in last week and they had some type of clicking noise. I test drove it and noticed when your going faster you don't really hear it. I pulled it in and checked the oil he had about a 1.5qt. So I did a routine oil change and bam the clicking is gone. So try that, that may or may not be your problem but its worth a try.

i had a oil change about a month and a half ago and i have bout 80k on my car so i use the synthetic oil .. i dont change it untill every 6k

They have adjustable lifters, and if they wear enough they will tick until you get them adjusted. 2000 Corolla, same problem, also had an exhaust manifold gasket leak.

add more oil if it clicks still u may have shot a rod through ur engine