grinding noise from tranny?

I just bought a 1992 chevy k1500 5-sp manual 5.0 v-8 (183k mi). there was a grinding noise that seemed to be comming from the transmission. It only happens in first or second gear, when you give the engine a lot of clutch. If you let the clutch spin a little and then go, it does not make the noise. Once its in gear and the clutch is fully engaged, you never hear the noise. already put new fluid in the tranny, seemed to help a little. Could it be the clutch bearing???? Thanks for any info