2000 Chevrolet Impala scrubing sound

Can you hold your computer closer to the car so I can hear the noise? Better yet, you need someone to open the hood and listen for where the noise is coming from. You listed two valuable clues but no details. Shifting into drive suggests the engine is rocking, and a pulley could be rubbing on a splash shield or some other bracket. I can't see that over a computer. An engine mount could be broken or collapsed too. A splash shield could be bent, loose, or mispositioned. "Foot on the brake" doesn't help. Is that while the car is moving? Standing still? Only when turning?

A number of possibilities come to mind. Shaking engine suggests a misfire, however, your Engine Computer should detect that and set a diagnostic fault code indicating which cylinder is responsible. That will turn on the Check Engine light too. Even when there's no misfire, a collapsed engine mount can allow a vibrating part to transmit that normal vibration into the passenger compartment. A potential clue is the severity of the vibration will change when you increase engine speed just a little.

Most of the things that can cause what you described are relatively not serious, but can become a bigger problem if they're ignored. Have a mechanic look at it so at least you'll know the cause. He will suggest a course of action, and I can offer a second opinion once I know what is wrong.