When backing up and sometimes turning right my brakes(?) make a squealing sound. Almost as though a pebble is caught and grinding on something. Honda 2004 accord-50.000miles. I was told I needed new brakes but the sound never happens when I use the brakes.

A grinding or rumbling noise can also be symptoms of a wheel bearing or constant velocity joint in a driveshaft. A worn wheel bearing can also cause a 'whistling' sound (as can a worn CV joint).

A grinding noise with brakes is either worn pads causing metal to metal contact on the brake disk/rotor, or the brake backing plate catching on a spinning rotor ... or a loose/missing anti squeal brake shim (they stop the pads from rattling and vibrating).

However, as you say a mechanic has looked at the brakes and can't find anything wrong .. I think I would begin to suspect a wheel bearing or constant velocity joint on the driveshaft (front wheel drive cars).

If the brakes are making a clicking sound when the brake is applied, that means that something may not have been put back together right. I would definitely yank it back apart and check to make sure that the brake pads fit securely in the brackets with no play at all, too. It's easy to get the wrong pads for a Sport Trac; the parts are completely unique and a lot of parts stores even have incorrect listings for brake and suspension parts for those things. Brake system wear can create a grinding, pulsing, or squealing sound, but shouldn't produce a click. Something isn't right there!

Generally any grinding you hear or feel from the brake system is a good indication that your brake pads have worn low and brake service is needed. Sometimes you can also get road dirt like pebbles in between the rotor and pad and it will make a temporary noise. I would have the brakes all checked though, for your safety.

Sounds like the brake pad wear indicator tab on the inner brake pad as the pads sometimes wear out unevenly due to stiky brake calliper slides. You would have to remove the wheel to inspect it.

built into the brake pads is a small bit of metal that when the pads get to low to be safe , runs on the rotor and produces the squeal applying the brakes stops the vibration so the noise drops off

what about replacing the failed wheel bearings that ids allowing the rotor to hit the brake calliper
the grinding sound is the rotor grinding away on the calliper or worn out brake pads

You state you changed plugs and wires - Do distributor cap & rotor? If not you should then set timing. That should cure hesitation (might change fuel filter also and run good fuel system cleaner through it)
Prob 2 - sounds like a u-joint or possible brake pad/rotor issue. Does the squeal only happen in mornings when cold? Sometimes after sitting overnight, rotors get condensation and when backing out they'll squeal/grind. Somethings to look at...

Squealing usually indicates that the brakes are in need of replacement. There is a small piece of metal that as the brake pads wear comes in contact with the metal rotor. When the pads get close to being worn away the tab touches the rotor and it squeals. The tab can also click.
When the pads are worn away completely the metal backing comes in contact with the rotor and it grinds. Grinding is bad. It means the car's brakes are metal to metal. This will cause damage to the rotors resulting in an even more costly brake job.
You should have it taken care of ASAP.
I hope this helps.

from my experience its sounds like ur front rotors may need resurfaceing...if ur doing that...may as well replace the brakes on the front as well...sometimes glazed front brake pads may make a sound but never heard of it as a grind, usually its a squeal...have ur dealer check ur rotors for hot spots in which u would need them replaced if they are overheated..also check the front pads for cracked brake pad material

Yikes! Do I understand this? You've had the grinding noise for 3k miles? Well, too late now, but you should have gone right back to the tire installer, and asked if they could pull the tire off and take a look. They probably wouldn't want to, but it sounds like they may have had something to do w/ this noise. (but I really don't know what could have happened) Sometimes a small pebble can get lodged in the brake rotor and shield, but it will fall out (sometimes) when you back up, or it grinds down enough that it just falls out on it's own. It wouldn't still be there making noise. Does this grinding happen only when you put the brakes on, or all the time? I would recommend a visit to a trustworthy garage for a check asap, as if it is a brake problem, you should have it fixed right away. Let me know the answer to my above questions, as I'd like more info to figure this out. Let me know how you make out. countrycurt0