Toyota 2000 Sienna makes noise in area behind air filter

This weekend I changed the wires, boots and spark plugs on my 2000 Sienna. It has around 305,000 miles and so far no problems. After changing the wires and spark plugs, I took it for a test ride; everything worked fine; when I got home I parked in the driveway; left the key in the ignition in the position where you can open/close the windows; before start and I heard a noise like ‘caboom’; I took out the key, put it back on; turned it before start; and the noise again; I opened the hood; checked for any sparks from the wires in the front and back; with the assistance of my friend I found the noise come behind the air filter, I thought that maybe because I needed power steering; but that is not the case; I added more power steering fluid; and it still making the noise. That area behind the air filter was not touched at all to change the wires and spark plugs; it does not make sense to me. Do I need to have a code reset after changing wires and spark plugs? Any idea where the noise may come from?

Are you sure you’re not hearing a backfire, which could be caused by an improperly gapped spark plug?