1998 Honda Accord NOT SURE WHATS GOING ON

I JUST RECENTLY REPLACED MY WATER PUMP, THE MECHANIC ADVISED ME TO REPLACE THE TIMING BELT AND THERMOSTAT SINCE THEY WERE GOING TO BE WORKING ON THAT AREA SO I DID. WHEN I DROPPED MY CAR OFF MY CAR RAN FINE, WHEN DRIVING IT WAS A SMOOTH RIDE WITH NO PROBLEMS. AFTER PICKING UP MY CAR FROM THE AUTO MECHANIC I NOTICED WHEN I WAS DRIVING AND EVERY TIME I PRESSED ON THE GAS PEDAL IT WOULD MAKE A NOISE. THE SOUND IS SIMILAR TO WHEN YOU HAVE AN EXHAUST SYSTEM ON YOUR CAR. AS I WOULD NOT ACCELERATE MORE ON THE PEDAL THE CAR WOULD BE FINE AND SOUNDS SMOOTH BUT EVERY TIME I PRESS ON THE PEDAL IT WOULD DO THE SAME THING OVER WITH A VIBRATION TYPE SOUND. I TOOK IT BACK TO THE AUTO MECHANIC THE NEXT DAY AND ASKED HIM "WHY WAS IT MAKING THAT NOISE? WHEN I DROPPED OFF MY CAR TO HIM IT WAS NOT MAKING SUCH NOISE BEFORE". AND SO HE AND HIS BOSS DROVE IT, AS HE PROCEEDED TO TEST DRIVE THE CART I TOLD HIM TO PRESS ON THE GAS PEDAL THAT IS WHEN IT DOES IT. WHEN THEY CAME BACK HE LOOKED UNDER THE HOOD AND HE TOLD ME IT WAS THE MOTOR MOUNT AND ONE OF THEM NEEDED TO BE REPLACED. I WOULD LIKE TO KNOW IF THAT IS TRUE, WOULD THE MOTOR MOUNT ON A CAR MAKE SUCH NOISE AS YOU DRIVE? WHATS WEIRD IS MY CAR DIDNT SOUND LIKE THAT BEFORE AT ALL AND NOW IT DOES. DONT KNOW WHAT TO THINK. HELP!