2011 GS350 RWD - Grinding Noise

[M.E.]

2011 GS350 w/ 176k miles.  Bought it used 2 weeks ago.  It drives beautifully except . . . .  with the car in motion, starting at about 25mph on up to 80+ mph, a metal-to-metal grinding noise is heard in the cabin.  With the car not moving, in Neutral, and revving the engine it does NOT manifest.  With car in motion and slipping it into Neutral, the noise does NOT change.  Varying speed (25-80+mph) does NOT change the pitch or loudness of the sound.  A Lexus shouldn't be this noisy - it is my 3rd.  The transmission fluid was just topped off.  Wheel bearings?  Maybe it is the Bridgestone tires about half-way through their life (but changing speed did NOT change the sound) ?  Not putting on my traditional Michelins just yet.

Any thoughts?

[RX400h]

Typically, a bearing-related noise will increase in loudness as the vehicle is rounding a curve, either to the left or right. I guess this can happen while the vehicle is going straight, but it is less likely to do so.
Any mechanic should be able to pinpoint whether a bearing is the culprit.

[Bykfixer]

Is it a scraping sound? Rattling sound?

Rattling would probably be a loose heat shield or similar somewhere along the exhaust pipe.
Scraping sound should change pitch as the speed quickens. You say it does not.  So it could be an exhaust hanger allowing the pipe to rub back and forth. 
 

My 'guess' is it's exhaust pipe related. 

[M.E.]

Thanks for the replies. I'll take up the exhaust hanger issue with my mechanic.

[RX400h]

8 hours ago, Bykfixer said:

Is it a scraping sound? Rattling sound?

Rattling would probably be a loose heat shield or similar somewhere along the exhaust pipe.
Scraping sound should change pitch as the speed quickens. You say it does not.  So it could be an exhaust hanger allowing the pipe to rub back and forth. 
 

My 'guess' is it's exhaust pipe related. 

Grinding noise 😉

[dcfish]

Is the sound front or back of cabin ? Left or right ?  Have some one ride along for better description of said noise. 4 ears are better than 2....