Hi! Lately Ive noticed that after driving my car for a few minutes, when I come to a stop and the engine is still running, the engine will *click/tick* once and then whirr/purr for about one second immediately after, then silence, then will do the tick/purr cycle again after about 3 seconds. When the car is in motion the surrounding noises are too loud to hear if the engine continues this cycle, but Im 80% certain it does this even while moving. Any ideas what this could be? It has been going on for quite a long time.
The click sound is very apparent if one is standing outside of the car, but the whirr is something I really can only hear whilst sitting inside of it. It sounds almost as if its the cars "inhale" noise, as silly as that sounds, as if its trying to breathe or suck up something.
There is a tool you might be able to borrow or rent from an auto parts store that borrows them called the "Chassis Ear". It is a set of six microphones, a switch box, and headphones. You clip the microphones to suspect points, then drive around while listening with the headphones. You can move the microphones around to zero in on the source of the noise. Be aware that many mechanics have never seen or even heard of this tool. Suspension and alignment mechanics use it to find rattles, squeaks, and other noises.
My guess is you're hearing an emission control device cycling on and off. Rather than trying to stop the noise, look for a missing cover or noise silencer. A stethoscope also works well if you can hear the noise while the car is standing still. You can find them at Harbor Freight Tools and any auto parts store.