Recently i notice some grinding sound when i m driving esp when the accelerator press and when during cruising,but once the accelerator is released the grinding sound gone,when i step on accelerator again to gain speed etc the sound is back again.what is the most likely cause.thanks.BTW my ride is GD1 manual,MTF changed,clutch changed

 

Sounds like a loose heat shield or baffle in the muffler is loose.

 

What john380 said was my first thought, too, particularly if the noise occurs mostly at certain rpms or engine load situations. If the noise also occurs when the trans is in neutral, then I guess you can eliminate the clutch as a source (a bad throw-out bearing is more of a "screech" sound I believe.)