grinding noise????

I have a 92 talon tsi fwd and there is a weird noise coming from my car, as soon as you step on the gas there is a grinding noise that you hear, however as soon as you let off the gas the noise goes away,but when the car is in nuetral and you rev it up there is no noise at all. I even put the car on jackstands and drove it in 1st 2nd and 3rd just to check if it was a tranny problem. My gears engage perfectly so i dont think its my tranny, no grinds at all, and i found out that both my front and rear motor mounts are completey broken, what could be the cause of this grinding noise, and i just replaced my axles with new ones.