I put my hand flat across the tread and felt around the circumference and didn't feel anything other than tread but maybe I don't know what I'm looking for. The tires have about 25K miles on them.

 

it is your wheel bearing. Mine went around 15K. Bad bearing or they forgot to pack them with grease at the factory.

 

Any simple way to figure out which it is?

 

A very worn bearing will show by jacking up wheel, and pulling and pushing at 12 and 6 o'clock on the rim. Alternating the 12 and 6 push pull. If you feel any play what so ever, you have a bad bearing. At 9 and 3 o'clock, if you have play you may have a bad tie rod end, ball joint, control arm or inner tie rod.

Check for cupping too.

I did a full write up on how to do a bearing and it can be found via a search.

 

I did try jacking one at a time, brakes off, and tried to feel for any play or any roughness in rotation but none stood out. Guess I could try again with what you have said in mind. It could be that I am just in the very earliest stages.

Thanks.

Steve

 

Do the 2WD RX have wheel bearings? I have the same exact road noise hum that the OP described, on my 05 RX with 68K miles. I thought it was the tires - I have Kumho Solus KL21 on them and they have about 10k on them. If it is a wheel bearing issue, what are the effects of delaying fixing this problem? Thanks.

 

i have a lexus rx 330 a 2004 model and i have to exact same problem. like when i go about 40 -50 miles an hour. i fell like there is sort of a mid pitched hummmmmmmmmmmmmmmm sound continuously. it never stoped it got anoying after a while. i dont know why. but it seems like it is coming from my back 2 wheels, but im not positive. the engine seems quiet. it just the road noise. i thought lexus were quiet cars which is why i purchased one.

 

Get the bearings replaced, any vehicle will be loud with bad bearings.

 

I will go for the bearings. Part 90080-36193
I will also check the rotors just to make sure they are fine.

Cheers

 

As an RX330 (2004) owner, I've had a wheel bearing replaced and now with Bridestone Dueler Alenza tires have a road noise issue after 15K wear in the tires, The noise was much louder with the bad bearing before replacement as I now have with the tires. As for Lexus quality, my RX was built in Canada and I'm not happy with the quality when compared to my 1998 Gs 400 which seems to be bullet proof as far a quality. The Rx 330 has already had 3 radiators and a wheel bearing after 57K miles. My next SUV will probably be a Toyota Highlander basically same as an RX for less $$.