Thumping noise when braking (DRIVING ME NUTS)

[audinoob45]

hello, I have a 2013 audi s4 prestige that I bought about a year and half ago. it has about 78k miles on it now. Bought it at 44k. Recently, my brakes started squeeling really loud. Checked it out and it was the brake pads. Changed all of the brake pads out to the Napa Ultra Premium brake pads. I did not change my rotors (Slotted EBC rotors all around) cause they seemed okay.

I got on the freeway the next day and noticed after braking a few times a thumping noise that got louder over a period of seconds. When I would press on the brake, the sound would go away, then come back again. It was getting EXTREMELY loud up to the point where I could hear it loud and clear and FEEL it in the brake paddle when I pressed on it. I had my friend drive next to me and she could hear it very loud too. Its a very loud thumping noise a if the brake pad is banging against the rotor or caliper depending on the speed I went. The faster I go, the faster the sound. the slower I go, the slower the sound. I realized that the whole steering wheel was shaking too as I was using the brake, so I changed out the EBC slotted brake rotors and got the NAPA Ultra Premium rotors all around. Made sure everything was rock solid and tight, and took it out for a drive. The sound didn't come back until I Slammed on the brakes a few times. Then once it came back.. I noticed it was from the driver side. this was the pattern of the sound....

1. No sound, I speed up to about 100 mph
2. Tap on the brake
3. Let go of brake
4. Sound is very loud
5. Stomp on brake and sound goes away
6. Let go of brake and sound comes back
7. Slowly push the pedal about an inch down and the sound gets louder.
8. Let go of brake pedal completely
9. Sound starts to faint over time as long as I don't step on the brake again
10. Sound disappears and comes back at random times (even if I don't step on the brake)
11. Can feel the thumping of the sound inside my brake pedal through my foot.

So I took apart all of the caliper and rotor again.. This time, when I installed the brake pads again, I put some of the red stuff on the back of the pads. Cleaned the rotors. Cleaned up the caliper. And put everything back together. The sound was much more faint this time. So I took it to two different mechanics. Both mechanics could not spot the problem. So, next thing.. I bought brand new pads (same exact brand) and took my old ones out and out the new ones back on.. the sound completely dissapeared for a couple days. Drove extremely smoothly. And today, I heard the sound come back for just about 10 seconds, and disappear again. Im about to burn this car down at this point, I changed everything out, and the clips that hold the pads are also working 100% fine, and theres still that sound.

Summary: Thumping noise starts after harsh use of brakes, it only comes when I press on the pedal and let go. Sound gets louder and louder before it starts to disappear. Can feel steering wheel vibrating HARSHLY when the sound is hearable. Car brakes very smoothly in streets and roads when driving normally. No shake or anything. Checked all the hardware, made sure everything is rock solid and tight before closing brakes back up. Probably opened and closed about 15x now. Nothing moves around when I physically try to move pads or anything with my own hands. Thumping noise is hearable from someone driving in the lane next to me. Coming from driver side. Tried changing out rotors and pads multiple times. The Red Stuff helps and the sound is gone for a couple days after use of it, but sound comes back after a couple days.

Assumption: Maybe its the caliper itself and its failing ? Unable to compress brake pad as quickly as it should ?

Note: As I'm typing this, I realized that I haven't done my brake fluid since I bought the vehicle. Maybe that has something to do with the noise ?

Please advise me anything you guys can. Ive tried everything, and spent a lot trying to figure this out. Its shittyy when you realize that you spent all this money on rotors when you never really needed any.

[jonwoods]

I would look at the bushings and ball joints in the front end, not the brakes themselves.

[Tyintegra]

This is just a shot in the dark, but COULD it be caused by the slots on the rotor catching in the leading edge of the brake bad?

Did you bed the new pads? I didn’t see you mention it.

[fitzydude]

How do the control arm bushings look, check for play.

[FastAudiS4]

Bushings. Mine are gone. I have the parts to fix it but I've been lazy lol

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[audinoob45]

I would look at the bushings and ball joints in the front end, not the brakes themselves.

If it was the bushings, wouldn't the sound continue even after I pressed on the brake? I can feel the sound in the brake pedal and it goes away as soon as I press on the brake pedal as if the piston just tightened the brake pad and stopped it from rattling.. thats where it confuses me. You're talking about the control arm bushings right?

- - - Updated - - -

This is just a shot in the dark, but COULD it be caused by the slots on the rotor catching in the leading edge of the brake bad?

Did you bed the new pads? I didn’t see you mention it.

The new rotors I have installed by Napa Ultra Premium are plain rotors.

[audinoob45]

Bushings. Mine are gone. I have the parts to fix it but I've been lazy lol

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I don't understand how the control arm bushings and ball joints is related to me putting my foot on the brake pedal causing the sound to disapear.
Im feeling it IN THE PEDAL.

I might change the caliper bushings out though.

[audinoob45]

https://www.uspmotorsports.com/Audi-...t-Audi-B8.html

This? ^^

[audinoob45]

If anyone knows please let me know asap.