I have a 2006 Mazda 3i touring and after getting the rear pads replaced about 2 months ago what I originally described as a grinding noise started (the Mazda service guy has since confirmed that's not actually a 'grinding noise' although that's the best description I know of). The noise only occurs when braking and it's a pulsating noise. The noise is coming from the rear and from both sides. The speed of the pulses is proportional to the speed of the car at the time it is braking. I don't hear anything at highway speeds (or perhaps other noises are covering it up) and at low speeds I don't hear the noise if I brake really hard.

The service shop: they have now done 2 complete brake jobs (new pads, machine rotors, etc, etc), put 3 different brands of pads on (the last pair they put on were OEM pads because Mazda told them some after market pads were causing the noises). They have spent hours trying to fix the problem, all out of their own pocket (the initial job was on my dime obviously).

The service place is a fairly large, reputation chain of shops and the folks have really gone out of their way, spending more time and money than I'm sure they would care to so I don't feel like anyone is ripping anyone off here.

Any thoughts? The Mazda dealer says you can't machine a Mazda 3's rotors but the shop where I went says, "yeah, that's what they all say when they want to sell you more rotors". But the Mazda service guy recommended I don't replace the rotors unless the rear end is shaking. Basically I don't feel like either are overtly lying but regardless one is still wrong. And that may have nothing to do with what's actually wrong with the brakes/wheels in the first place.

 

I've never heard of not being able to machine rotors.
What you describe sounds like the rotors need to be turned or a sticking caliper.

 

I'd agree that something is causing the pads to make continuous contact with the rotor, causing warping due to heat and premature pad wear.

I've found that turning rotor doesn't make sense from an economic perspective on my wife's Mazda 6 and other cars I've own. More prone to warping and then need replacing anyway (I haven't had to replace the breaks yet on my 3). Just my 2 cents.

 

A grinding or growl would probably be different from a pulse.

With a constant grind or growl, the rotor is at least not warped yet and it is just a constant contact. You said it is only under light braking. So the pads may not be seated properly in the caliper or not have the brake quiet on them. I had some bad DuraCrap pads on my truck that did this. The springs were not tight enough and they vibrated badly on light braking. If a caliper was sticking, you'd smell hot brakes before you'd hear anything I would think.

With a pulse, the rotor is probably warped. It could also be that the pads are not retained strongly and are vibrating. It could also be the brake system is pulsing. Maybe air in the system, a bad flush, a bad ABS sensor or connection.

It sounds like the dealer is feeding you garbage.

 

Weird: if the rotors aren't warped and the caliper springs are doing their job, the only other thing I can think of that would do that would be if the rotor(s) aren't lying in the same plane as the calipers. This would mean stripping things down and wire brushing all of the mating surfaces (especially the shoulders of the studs) to ensure they're perfectly flush.
If one wheel grabs, the action of the proportioning valve would probably cause repercussions on the other, by the way.
I take it your wheel bearings, rear suspension bushings etc. are in good shape, otherwise I'm stumped.
What happens if you leave the pedal alone and just haul on some handbrake?
I suppose if all else fails you could put the car onto a track to spin the wheels and see if it can be located that way.

 

Well you all were correct. The tire place machined the rear rotors again, this time doing something different and the noise has gone away. The partner where they get their aftermarket parts from stopped by and had the machinery to turn the rotors and they used their machinery to somehow machine them differently (don't ask, I have no idea). Anyway, they claim they had machined them at least twice over the past month but this "new way" made the difference the other 2 turnings didn't. Anyone think there is a reason I ought to give this shop another chance with my next brake job?

 

Well it seems like they are a dime a dozen. Now they know the best way to go about it but most importantly they helped you though your problem. I only wish I had a dealership or mechanic that I felt that confident in that I know would help me out until my issue was resolved (on there own time and money). So I would personally give them another chance!

 

I agree.