With the engine turned off and the switch opened, a buzzing can be heard on the left side. It is similar to the noise cicadas make and, to listen to it more clearly, you need to open the hood. I think the noise appeared after the engine was cleaned. What can it be?
The sound might be coming from a contact or fuse that got wet when cleaning the engine. Try driving the car for some days so that the water that might be present evaporates completely. If it does not disappear, you should take your car to be checked thoroughly.