Mounts also make a lot more noise in addition to vibration. I have driven several vehicles with issues and I would know it.

The other area that can sometimes cause this wobble (and I have had this problem on both sides of my RX300) is the front lower supports, specifically the bushings near the wheels and they can go.

What you have to do is lift the front side of the vehicle up and shake the wheel and see if there is any play. You can also move this piece that I have shown the location of below and see if any movement.

Although I still agree with Lil4X, there is an outside chance that this wobble I am describing could be occurring and the shift change at about 40 mph might be enough to give a little jarring to these bushings (that can get worn down from the road, potholes, bad roads, etc.)

 

while reading your posts (btw thanks for the replies), ive noticed that using trembling is not the right word, its more of a wobbling, like some have used here. but i will check the car today

 

I just picked my new RX over the weekend and as I was driving home from the dealership (about 2 hours away), I noticed the similar vibration folks are describing here. The vibration is most noticable in the steering wheel at around 70-80mph and it starts around 50mph.
I'm bringing into the dealership before end of week. I hope it's just wheel balancing and rotation... don't really want to have to compromise and live with it.

 

since i started this post, i have 4 new tires under my car and everything is fine now.

if you just got your car, check your tire pressure. most dealers over inflate the tires.

 

thanks for everyone's response.... here's an update at the dealership. The dealer balanced on all 4 tyres (I suspect rotation was done too but could not confirm). The vibration is now gone.
After picking up the vehicle I noticed a 'ticking' noise from the driver side a/c vent and dash area right behind the steering wheel. Every minute or so, it will do a 'tick'. To me it definitely seems that the a/c vent piece and the odometer piece is not properly sealed with the dashboard. At first I thought adjustment was made to these areas to fix the steering vibration but the dealer confirmed that only the tyres were worked on (interior was untouched). I'm debating if I should bring it back to the dealership since I'm not sure what the dealer would do to fix it, or make it worse in the process(seen too many dash rattle horror stories).