So I was backing out and down a driveway last weekend in my 2015 GS, it was typical spring nippy weather in the morning and as the car transition from the driveway to the road, I can hear the roof flex a little. Sometimes when hitting a bump, I can hear the dash make a flexing sound. Minor stuff. I'm very sensitive to noises, more so in such a quiet car.

How does it compare to a BMW or Benz or Audi? I have not driven any of those vehicles to know. Is it normal or par for course among this class of cars outside of an exotic or RR or Bentley?

 

Creaking and rattling is due to torsional rigidity and bending stiffness, but it is also due to spring rates, low profile tires and build quality.

The current model 4GS has a very rigid body shell, unlike my old 3GS.
However, in the interest of sharper steering response and greater terminal grip, the current 4GS probably has the firmest spring rates in its class in base trim, to minimize weight transfer around corners.
Thus, the current model 4GS is possibly more prone to creaking and rattling than its competitors.

Despite using a much more rigid platform than my old 3GS, my new 4GS is more prone to creaks and rattles due to its considerably firmer spring rates, and less compliant springs for less shock absorption.
Suspension design is a compromise.

 

On my 2015, I heard flexing coming from the roof and it was constantly creaking while driving. I had it addressed recently by the dealer, and first they said it was the rubber seal around the sunroof but was surprised that a 2015 was having the issue. They tested a fix, but it didn't work so they were told to replace the entire sunroof. So one $4K warranty claim later, the problem is gone.

 

This is a quote from the Toyata/Lexus European newsroom bulletin when the 4GS hit the auto show floors in 2012. Statements from many auto journalists at the time was that the 3GS was quite rigid, but was prone to awkward body modulation at high speed, for instance door vibration as 200 kph was neared and passed. From what I read at the time the additional rigidity in the 4GS was achieved by additional welding. At least that is what I remember.

The only creaking in the dash I detect is at temperatures below -15C and the sound resembles kitchen shrink wrap, but only occurs before the warm-up of the interior. I have recently had an empty passenger seat vibrate, but that seems not to be occurring now.

 

They actually made the 4GS' waistline higher.
The higher the waistline, the greater the cross-sectional surface area, and the greater the rigidity.
Making the waistline higher, while all other factors are the same, is like having a thicker piece of metal.

 

It just surprised me a little that's all. Figured the roof is made from hot pressed steel, more welds and more adhesives aiding in the extra structural rigidity. Otherwise its a nice drive and solid.