Slight noise from the engine from moment you start the car

[K_350gt]

I own a Nissan Fuga 350-GT, every time i would start the car, the moment i drive and as soon as it gets to the 1st gear, there is a sound that comes from the engine, like a slight knock/noise. This only happens when i give the car a rest of about 30 minutes or more, either way. I use Castrol engine oil and i can't remember the model but it wasn't 5W-30, could this be the reason? I'd really like to know what the problem could be and a way about it. Thank you all for your time.