I have always wondered what makes a car groan under the following conditions. You are at a full stop, A/T is in drive, and your foot is on the brake. You lift your foot slowly, but not enough to allow the car to move. That’s when you hear a groan from up front. Would you suspect brakes, suspension, engine mounts, ABS, or anything else?
Definitely brakes, and since this phenomenon existed long before the advent of ABS, we can’t blame modern technology for it.
Could also be shocks/struts compressing or decompressing as the car’s weight shifts from front to rear or vice versa.
Brakes. The reason your engine can continue to idle with the car in D and your foot on the brake is that the energy from the engine is being dissipated by the torque converter (TC).
The TC is like a bagel cut in half, hollowed out, and having vanes on each side and fluid in the middle. As the front half spins, driven by the crank, and the back half is held still by the brakes, the fluid in the middle becomes turbulant and builds pressures. The energy in that fluid turbulance is dissipated as heat via the tranny cooling system, the “transmission cooler” that is that little radiator in the car’s front.
In short, while you’re sitting at the stoplight, the front of the torque converter is trying to pull the back of the torque converter along with it via the fluid inside. But it can’t because the brakes are holding it. When you slightly release the brakes, the energy in the fluid turbulance overcomes the brakes and the discs begin to turn. The energy stored in the fluid is released. That “groaning” is a common side effect of that brake pad friction being overcome just slightly.
As VDC said, while ABS can be blamed for other unpleasent noises, this one isn’t the fault of ABS.
That noise is the brake pads making contact with the rotor…when you do this at very low…creeping speed you are simply hearing the pads vibrating against the mirror smooth surface of the rotor…Happens all the time and is very common… Nothing to worry about its perfectly normal… It means nothing.
Blackbird–this same noise happens with drum brakes as well. My parents had a 1952 Dodge with the “lift and clunk” semi-automatic transmission when I was in high school. It would make this noise when one was trying to hold the car with the brake.