- Correct, most of the sound you hear is in fact the injectors, but the engine will sound quieter and more smooth with a good quality thicker oil.
- I recommend changing the oil every 5000 miles if you do city driving, this way you wont need to clean out the passages very often.
- every occasional oil change, try using some shell rotella 5w40. Its not only a very high quality yet cheap oil, but it has detergents which will help keep your motor nice and clean.
- in Australia, the owners manual specified anywhere between 5w40 - 10w50 so dont be scared to use slightly thicker oil if you live in a hot climate or drive aggressively
-you said that you were listening to the idle for 10 minutes? The less you idle the better for your Engine. Its always best to just get in and start driving right away.
- liqui moly is a good oil, but if you want the best toughest oil for your car I recommend motul. Very, very good oil. I suggest you also avoid Mobil 1.