Hello, I drive a 2007 EX-L 4 cylinder 4-door sedan with 29k miles. Just yesterday I was running a few errands and after been driving for quite some time (over 30 min), I heard an odd harmonic humming noise coming from the rear of my car. The humming noise will last for about 7 seconds or so and then stop (while driving).

I parked my car, went inside a store for about 15 minutes, came out and was driving home when the noise came back AGAIN for the same amount of seconds. I have been driving the car for about 5 minutes after I started it.
Then, last night I went out and was driving for about 5-10 min and the noise repeated itself again.

The first time I heard it I thought it was a huge semi truck following behind me, but there wasn't. I even shut off my stereo and A/C to hear it better all three times and confirmed it was definitely something from the rear of my car. It sounds electronic to me, like something turning but it's a constant-pitch humming noise that only lasts a few seconds.

I don't know if my speed or RPMs have anything to do with it. I don't know if it has to do with the ABS unit, I wouldn't know what that would sound like. I don't know how to replicate this sound to the mechanic, so I don't want to waste money there if it never happens while they're in my car...hence why I came here first I have NEVER noticed this when the car ignition was off.

Is this my fuel pump? can someone guess what is going on and how much it would cost to fix this?

My manufacturer warranty expired in October 09 even though I only have 29k miles!!!! aughhh and my accord should not be having problems at such a low mileage!!!

 

Check your rear brakes. They have little tabs that hit the rotor when the pads are wearing down. They make a screetching sound (like fingernails on chalkboard). But when they first begin to just barely touch, the sound can be real strange, almost musical. If that's it, it wouldn't have been warrantied anyway.

Other possibilities include wheel bearings, but I don't know why they would only make noise for a few seconds.

Fuel pump??? Maybe but again why only for a few seconds. Make a habit of turning the key to ON but not immediately to start. Listen for the fuel pump to run for 2 seconds. Compare that to the noise you're talking about. Keep doing that in case the pump makes that noise only rarely.

 

Your keyword here is harmonic. [Something like Pink Floyd's Welcome to Mahine?] If the sound seems to be occuring every 7 seconds, verify that the sound changes while turning. (even very slight turns). Does the harmonic change with increase or decrease in speed? Does it go away at any speed?

On a smooth curved highway, pay attention to see if the shound changes with left or right turns. If the sound increases or comes on during high speed left turn it could be your left rear bearing and vice versa for right turn.