Noise when backing up

[crazyman03]

I really dont have a better way at describing this so.. here goes.

 

My wife's '09 forester started a loud burrrrrrr/buzzzzzz sound when backing up. It kind've sounds like the sound you would get when low on power steering fluid except it only happens when in reverse and regardless of actually moving. Yes, I have checked my fluids and am not low on power steering or brake fluid.

 

I ran into this sound once before on a buddy's car that ended up going away when we did a caliper swap on all 4. Any ideas? Braking is fine, pads are fine, fluids are fine. it just does it when in reverse only. 

 

Ideas? I'll try and get some audio of it later

edit: i just tried to get the sound to record and it didnt do it unless i was moving in reverse so, scratch the whole not moving part. 

-Justin

[1 Lucky Texan]

can someone pace the car outside while you go in reverse? (be safe) Try to find which corner or see if it's 'central' or from the engine bay....

long-shot guess, some kinda debris between backplate and rotor.

[crazyman03]

I had thought about that. It doesn't make a sound when jacked up. 

 

As far as location, it sounds like passenger front. 

[1 Lucky Texan]

hmmmm...abs pump may be in that area......???

[idosubaru]

Does pushing the brakes or letting off completely change the noise?

Straight or turning the steering wheel change it?

Is it electrical (some device buzzing) or mechanical in nature?

[Ferret54]

Have you replaced either of the front drives shafts?
I had a similar noise on a 2001 Outback our daughter owned a few years ago, turned out to be a replaced passenger side front drive shaft. little too much play on inner DOJ joint. Was a Cardone replacement. Other than that noise when in reverse and NOT moving ( loud hum, rattle sound, made door panels rattle ) car drove normal with no other noises  or vibrations.

[crazyman03]

I know this is way late (like, a year haha!) but I hate reading unresolved topics for solutions so i'm posting what it was that took care of my issue - 

 

After a while, it came time to do brakes and I bought a pad/rotor kit for all 4 corners. That is what ultimately took care of the noise. The piston on the driver front caliper didnt look fully out, however i speculate that it was the caliper making the noise. 

 

So thats it!, replacing pads took care of it. I dont think that rotors made that much of a difference. I only replaced mine because i never did in the 5+ years of owning the car and i wanted them done. 

 

-Justin

[idosubaru]

Thanks for followed up.  Good to know and have for the next person. 

If the dust shields aren’t bent, it’s due to rust on the rotors. 

Hitting them with an angle grinder or Demel will fix it.  Or Turning the rotors will fix this as well.  do that and high quality OEM originals often will last the life of the car.

I’ve done it with a Dremel and angle grinder more as a test to isolate where it happens. Not worth the time unless you’re a DIY minimalist purist, but I wanted to leave and isolate exactly what the cause was. Now I just look at those adjacent ridge and inner area right up where the edge of the pad will touch to assess and turn or replace them like you did. I at least learned how to replace only problematic rotors and not all of them for no reason.

The rotors get rust outside of the brake pad contact area. Like the clean area wiped by the pads stays clear. Just on the inside of this and just on the outside edge of the rotor will have a ridge of rust - sometimes not a very big one.  

some minor change (someone working around the area, new pads, dirty or tweaked clips) can cause the pads to start just nipping at the edge of that rust  and causing a grind noise. Sometimes only when going backwards.  And this can be caused just by new pads having a slightly different shape or rotor contact due to the clips   

same with inside parking shoes though they’re a little less prone to rust due to less exposure.