While driving on Saturday, I noticed a high pitched, almost harmonic noise coming from the Sequoia. It doesn't change pitch with RPMs or speed, but seems to get louder the faster I go up until about 55 and then it goes away. I also can't pinpoint a general area that it's coming from in the vehicle. It sounds exactly like in this video (~7 seconds in you can really hear it). My wife called me today saying it was doing it and it was loud enough that I could hear it over the phone. I had her power the radio off as it sounds almost like feedback, but the noise continued. Any ideas on what this could be?