3 on the tree grinding noise

I just bought a 78 Dodge D100 w/ a sl6 and a 3 on the tree. It was a 3 hour trip to get back home and the truck ran great. Driving it to work today, I notice that I get this grinding sound down in the tranny/engine area when I'm on the clutch and I hit the gas. When I let off the clutch the grinding goes away. Doesn't matter if the wheels are moving or not, it'll grind as soon as I hit the gas with the clutch pressed in.

Anyone know what might be up? I still have the paperwork from when the guy had it fixed at the shop. I'll have to look closer at home but it looks like it has a new clutch, throwout bearing and the whole deal. New bushings in the column so it shifts tight. It's really my first manual transmission so I'm kinda lost when it comes to stuff like this. Thanks.