Accord vibration noise?

My daughter’s 02 Honda Accord is making a sound like a phone on vibrate every few minutes as it sits parked in our driveway. Not sure if this is pertinent but the driveway is sloped so the rear is higher than the front. I’ve search everywhere to try to locate the sound (thinking it was a cell phone left in the car) but it seems to be coming from under the middle to rear of the car. Could it be the gas tank pump going spastic?

I think that one might be able to compare the sound of the fuel pump energizing to a phone on vibrate. This would be really odd behavior though. Pull the gas cap off & listen through the filler neck. If the noise is the fuel pump you’ll be able to hear it much more clearly. Or find the fuel pump fuse, pull it out & see what happens.