My IS350 has been pretty perfect so far. Within the past week it's started to develop a buzz which I find annoying, but it doesn't seem to affect performance. It seems to occur from the right side of the engine compartment, and occurs around 50 mph and 1.5 to 2k rpm, typically when going up a hill or under some sort of load. It's really noticeable when the radio is off.

It almost sounds as if a valve is loose and flapping? No idea what else it could be... Anyone have any idea? Gonna take my car in for service this week.

 

Has your car had the valve spring recall done? More info here...
http://jalopnik.com/5581813/lexus-re...-valve-springs

It might be related to that if you haven't had the valve spring recall done already.

 

Or a heat shield is loose.

 

yup, I had the valve springs done early this year so i don't think that is an issue. Is the heat shield the same thing as the engine covers? I know I have a few of those clips missing and haven't had a chance to replace them yet cause they're damn expensive =/

 

Now that you mention it I have a weird noise too but this is only when in D and stopped, like at a light for example.

Your noise is under load and 50mph. I wonder if it's the engine covers

 

i guess it is the plastic piece in side your glove box (on top of the tray) .