Not being able to hear your engine it is hard to help over the internet...if it were me I'd take the car in to have the service department listen to it. If they tell you it's ok than learn to live with it. By doing this you also establish a history...If it breaks they will fix it under warranty.
Also, does your hood have a heat shield (underhood sound deadener) like the SX's do? If not you might want to get one installed on your EX -- might help to quiet things down.
Also, does your hood have a heat shield (underhood sound deadener) like the SX's do? If not you might want to get one installed on your EX -- might help to quiet things down.