scraping noise when backing up

I have a 2006 Tacoma xtracab 2WD, 94,000 miles. I hear a faint scraping noise when backing up. I only hear it when I am applying a little gas while backing up. If I don't apply gas while backing up I don't hear it. It sounds like it is a faint scrape about every wheel rotation.

I did have a shop look at it; they couldn't hear the noise (it was snowing and I hadn't determined that it was only when applying gas) but they did check the brakes and they were all fine.

Any ideas? Thanks.

 

rock stuck in dust shield?

 

got new tires or wheels? Might be a little tire rub on the mud flaps...

 

Other parts that could be rubbing and making the noise are brake drum, driveshaft. And if you got super fat tires then also check the inboard clearance from shock mounts and leaf springs, etc.

 

No new tires, and they are small tires so no rubbing. Where could the driveshaft be rubbing?

 

Check the u-joints, and grease them.