Grinding noise when coasting?

What is your question?

Just bought this car ~1 month ago. A week after that it stopped accelerating. Got it towed to mechanics and the catalytic converter replaced. Now it accelerates but I've noticed a grinding sound when coasting. When the car is stopped and I let my foot off the brake, but before I hit the gas, it grinds at about 1500 RPM. Once I hit the gas and accelerate, it stops. I notice it faintly while I'm braking, again at around 1500 RPM but it's loudest while coasting. Someone said it could be the drum brakes, someone else said maybe the transmission.