Today when i was driving my car, i notice some weird noise coming from my car.

It make the noise everytime i accelerate, the weird thing is, it only happen when it accelerate from standstill or low speed (at least that's the point where i can hear it).
Very noticeable when going uphill.

It doesn't make that noise when i rev the engine in neutral.

The noise is similar to when u drop the clutch a little early in manual car, sth like soft vibrating, but can't feel it inside the car.

My car is automatic. Could it be transmission problem??

Any ideas??