what is this horrible sound my car makes?

I drive an automatic with disc brakes. The sound only happens when I’m idling at a stop sign or red light (in D, but with my foot on the brake), and then step on the gas to go. There’s a loud “THUNK!” that comes from the general area of my right-front wheel.

What the hell is it? I imagine it’s the brake “sticking” to the wheel, but is that possible or likely?

Sounds like your brake pads are sticking. Could be a collapsing line, or could be a problem with the pads or rotors. I’d take it to a shop and have it looked at.

Sounds like the brake pad may be sticking to the rotor for some reason. Take it if in you are not up to checking it out. If you are up to it, jack up that corner and take your wheel off and take a good look at your pad, rotor, and caliper. Can’t really speculate beyond that, but brakes aren’t too complicated and it should be easy to figure out why this is happening once you look at it.

It could be from looseness or wear in a suspension part, or possibly even a front drive axle. There would often, but not always, be a corresponding noise when first braking or decelerating. I won’t say it’s impossible, but it’s not typical for a brake problem to make the kind of noise described.

My guess is a broken engine or transmission mount. As you step on the gas the engine and/or transmission is shifting forward or backward and is causing that thunking sound you hear.

Is the car front wheel drive? Might be a bad constant-velocity joint.

Try to do exactly what you do, but with the car in park (that is, rev the engine about as hard as you would to make the sound, if it only happens when the engine is warm or cold, make sure it’s under the same condiditons). If it still makes the noise, it’s not the brakes. Is there a steep hill around? If there is get up to the top (but with the the car heading back down). Get the car to a complete stop, put it in neutral, shut off the engine and take your foot off the brake. IF it get’s going quick enough and makes the sound, this would help isolate the problem to the brakes/suspension/CV (in other words, it would help rule out tranny or engine problems). To me this doesn’t seem like a brake issue, but it’s really hard to tell with out being there. Also, if you take the wheel off and putz around with the break your self, remember the discs will be HOT if you’ve been driving around. One more thing. Try to get a friend to stand outside the car (maybe even kneeling down next to that tire) when it makes the sound. There is a chance it just SOUNDS like that’s where it’s coming from.