my engine is making a diesel like engine noise after the car has been warmed up at idle. when i just start the car the engine sounds normal but when it warms up and the rpm starts to drop around 1000rpm the engine starts making the noise..the oil level is good so it can't be the oil.. Is this normal on all g35 engines or is there something wrong here?

And another noise is when i'm driving for a while and then i stop the car and put it in neutral and then i turn the steering wheel to the left and right i hear some kind of ticking or chattering noise as i'm turning the steering wheel and the rpm starts going down a little and then back up. The noise seems to be coming from the engine when i'm turning the steering wheel.