I have a 2009 RAV4 and it sounds like I am driving over a grooved ssurface when I accelerate between 35 and 45mph

How many miles on the Rav4?

145,000

http://www.rav4world.com/forums/85-4-1-faults-fixes/60946-bad-propeller- driveshaft-u-joint-need-replace.html Read the posts at the link. It is possible that it is driveshaft related.

Thanks I will read on this because it is getting frustrated not knowing what it is

No guarantees, but a good place to start.

While not likely, check your tires: there may be low pressure in one or more. Also check both side sides of each tire for any "bumps" or "bulges" and for uneven tread wear. Old shock absorbers/struts may be another thing to check out- if they are weak that can cause suspension and alignment problems which can cause noises. Oh IMO, the mechanic that could not help you, needs to be replaced on your list of "who the go to", by someone that can at least give you good information, suggest a correction and give an estiment of the costs, so you can decide on a course of action (my 2 cts)

I have the same problem...What is the propeller???? I know what a u-joint is and a drive shaft but never heard of propeller??????

181000 miles. Having same issue. Just had CV joint hub replacement and axle. Still having issue. Mechanic is not sure where to look next.??? Help

the mechanic i went to couldnt find anything either so now theyre recommending a new transmission. same issue though with my 2009 rav4 - 1500rmp between 35-45mph sounds like a rattling/vibrating.

Same issue!! I have a 2011 rav4 with 125,000 miles. It’s always around 1500-1600 rpm and stops if I take my foot of the accelerator.

2010 with 130k, starts about 40mph, stops once accelerated past....no other issues, mechanics don't know what it is. Annoyance at best, ignoring as it appears to be a common complaint from other searches on the internet.

This sounds like the "torque converter shudder" issue. Rav4world has plenty of resources on the topic.