I drive a 2008 Honda Odyssey with 102K miles. On my way to work this morning I noticed what sounded like a humming/buzzing noise from under the hood. I thought it was the car in front of me at first, but then discovered it was indeed my car when I made it to a stoplight and still heard the noise. It sounded like the engine was revving or staying revved even though the car was idle. The RPMs never changed to coincide with this revving while idle. I eventually got off the interstate when it became worse and pulled over into a parking lot. The car continued to make the noise, although not as loudly while parked. I opened the hood and the noise was coming from the left side of the engine near the fan that has the belt (I'm assuming this is an engine cooling fan, but I have no clue). I turned the car off and let it sit for about 30 seconds, then cranked up and went about my way. The noise pretty much stopped at that point.

I'll probably go have it checked out today anyways, but wanted to see if anyone else has had this issue before and if so, what did it turn out to be? We have an Acura MDX as well and we've had transmission issues from that and we had a PT Cruiser before the van that had transmission issues, so we're hoping it's not a transmission issue and is just a simple cooling fan or sensor switch. There is no grinding like our PT and MDX had, just that audible revving engine noise.