Hey there
A couple weeks ago I bought a 2004 Honda Civic EX From a used car dealership. It was doing fine until a week or two ago it started making a weird sound when I would shut off the car. Now it makes a weird sound when I shut off the car AND when the car is turned on, it screeches for a minute or two then goes away. Could it be the aftermarket air intake that is in the engine or what? it never did this and now it is doing it... what is going on with it?

Here's a video of my engine:
2004 Honda Civic EX Engine Sounds - YouTube

 

You probably just need some belt dressing.. give it a couple of drip of aft or oil on it..