Annoying brake issue - what could be the cause?
 

I am the original owner of a 2012 Mazda 5. Since last fall I’ve had a strange braking issue. Basically whenever I am slowing down to a stop on a rough/gravelly/bumpy road, I feel a vibration or pulsing below the brake pedal, along with a sort of metallic sound at each pulse, kind of like a grunt. (No vibration at steering wheel or anywhere else.) Or, if I am slowing down and then I go over a little bump, I feel a bump under the pedal and the same vibration noise. I’m not sure if it’s the ABS being over-sensitive (although an ABS indicator does not turn on) or something else that is wrong with the brakes. I've driven this car for almost 7 years so I know this braking behaviour is not normal.

Last fall when the problem originally occurred, they diagnosed it as warped rotors and replaced the parts under warranty since they were only purchased a year earlier. This actually seemed to fix the issue at first. I did a tire change to my winter tires and the breaks were still fine.

However in the middle of the winter the problem started happening again. After winter was over and I swapped out my winter tires to my all-season tires, and the brake problem still remained. I took it to the dealership a few weeks ago and asked them to inspect the rotors again. They said they looked brand new and didn’t need any servicing.

Then, about a week ago I went to a supervisor at the dealership to show him the problem on the road. I ended up driving him around town for over half an hour, along roads that I travel on every day, but somehow the problem could not be reproduced. Ugh!! It was during the early afternoon and the weather was relatively warm and dry, and I wonder if that contributed to the lack of the issue. So I just assumed the problem went away… maybe it was dirt or something that had dislodged in the brakes?? I have no idea.

However the next day the problem returned again(!!) and I have been noticing it since. I don't know if the weather or humidity plays any part; I haven't observed a consistent difference. Nonetheless it's the same problem as I described in the first paragraph.

I am a novice when it comes to car knowledge, so I have no idea what the problem may be. Perhaps it’s an ABS sensitivity issue? Can anyone provide some advice?

TLDR; I experience pulsing with sounds under the pedal when braking to a stop on rough road. Was temporarily ‘fixed’ by replacing the rotors but problem has returned.