Hi, I bought a 2008 Lexus RX350 off a technician that worked for a Toyota dealership.  He said he was the main line guy that replaces engines and transmissions all day.  This vehicle had the engine blow due to the water pump not being replaced.  He put a 2011 Toyota Highlander engine in its place which had around 149k miles on it the body of the car has 99k miles.  He swore everything was great on the car and the transmission wasn't damaged he put a new radiator in the vehicle, but when I hooked up my computer to the car I could see the long-term fuel trims were only allowing the car to get 16-18 mpg when I think it is rated for 22 mpg.  I shouldn't have bought it my main issue is around 60+ mpg I start hearing a strange rattle.  I've tried everything to figure out this rattle.  First I took it to a shop and they charged me $500 to replace an inner tie rod on the rack and pinion, but the car still made the noise. Here are the repairs/replacement parts that I've put into it myself to avoid costly shop costs:

• Replaced the rack and pinion
• Replaced front sway bar bushings
• Replaced Front Lower Control Arms 
• Replaced struts on all four tires
• Replaced Sway bar links in front and one in the back (one side was stuck a bit too hard so I just left it for now)
• Replaced balljoint and wheel hub assembly in the front both sides
• I put some foam with HVAC tape around a hose in the back of the engine bay since it was the only loose part that I could find to prevent it making noise
• I made sure all the existing engine covers of the bottom of the engine were properly mounted and secured them further to ensure no wind to making them rattle
• I put some rags on the plastic mount on the spare tire in the back since I could see wind would make it rattle
• Ziptied one spot where some plastic bezel screws had come off over the years and replaced most of these as well
• Replaced the transmission engine mount (was required since it froze up when replaced the front lower control arms)
• The car has been aligned four times and is as smooth as a dream
• I'm bungee corded the top luggage rack
• Sprayed anything metal with white lithium grease and any bushings replaced
• I checkthed the drive shaft ball joints they both appear solid no rattle there

I got that noise detector that Scotty shows and hooked it up to the engine and transmission all over the car.  Oddly, the only real time that I heard the noise is when the noise detector was mounted to a front struct that had been replaced and these were torqued to specifications, so I think it is just picking up the noise as I would be hearing it since I could hear all the road sounds as well when it was mounted at the position.  There are probably some other things that I've tried as well that I'm forgetting to state since I've just lost my mind at this point.

The only thing that really still stands out in my mind is the transmission had some temp sensor not working from what I recall on the computer, but it isn't enough to trip a check engine light for some reason.

I had the noise master clamped to the transmission and didn't hear the sound, but it seems odd that it happens at a particular speed 60+.  Something worth noting I'm pretty convinced at this point it happens when it is really windy because I have even heard it at 45 mph on a windy day.  The noise seems to have reduced here lately somehow so something I did might've had some minor impact, but it is still there.  The only changes I've made lately add the rags under the rear tire and there was a computer module that wasn't clamped down in the engine bay by the main drive belt that I zip-tied down.  So, I think maybe some of the noise was coming from the rear tire plastic mount.  I in-fact took the bottom of the plastic mount for that rear tire completely off since it seemed like it wouldn't secure properly.

Attaching a video clip of the noise from when I originally purchased the car I think if can vaguely be heard around 40-50 seconds mark.  Any help narrowing this down further is much appreciated.  I'm mostly worried this is something to do with the VVTI rattle or the transmission going bad.  The guy that sold me the car told me valoline transmission fluid covers the transmission for 50k miles and that he had replaced the transmission fluid and the front differential.  The vehicle is AWD.  I starting to wonder if it is something weird like an engine mount maybe the rear that he just went cheap on when putting in the replacement engine.

https://drive.google.com/file/d/1uehfdyiXwt9Oe8W9zPDx4X72RI5CCDRY/view?usp=drivesdk