I've got a 2006 Prius with 199k miles, and it has developed a strange rhythmic noise when accelerating. If I'm driving over 35 MPH, I can hear it. It starts out slow, then gets faster as I reach higher speeds. Here's a video I recorded on my drive to work this morning, you can hear it fairly well. Any ideas? I've checked the oil and the air pressure in the tires, and everything was OK.
I am not sure if the Grinding noise is coming from your units background noise, but if you have grinding noise then definitely check your wheel bearing. I also hear a rattling noise or tapping noise, if tapping noise then I would have the car in park and activate the motor to see if motor issue, but if you only get the noise when in motion than check your hubs and see if your wheel is choppy?