Reverse to drive: Grinding, winding -then clunk

Nice titile huh?

So I just bought a 96 4dr blazer LT with 52k on it (auto tranny). Nice right? Not so, I have already had electrical issues, alternator and plug wires BUT:

When I let the car sits, say at work then go to pull out I put the car in reverse then to drive I hear a grinding like the car is still in reverse but its in 1st gear!!???!!!??? If I speed up the grinding will increase with speed and it WILL NOT stop until I slow to a stop. At that point in time the noise will go from grinding to a loud "clunk" like it is kicking into gear.

The ????????????s are its already IN GEAR? How does it clunk into gear twice?

I checked the trans fluid and it is clean and full (hot). I just spent the dough to buy it, the new alternator, new cap, rotor, wires, plugs, pcv, oil filter, fuel filter and tires. @ 52k I though I wouldn't have to spend any more money on it.

Any ideas before it goes in?

I plan on taking it in for a tranny flush, filter, fluid change. But I would like to know if anyone has any ideas before I go.

I have all the repair records and I see topped off trans fluid at a random intervals but nothing else. It was froma family member so I don't think I got screwed.. yet. THanks in advance.

Stinct.

Sounds like your transfer case is only partially engaged.

Have your transfer case checked out.

Offtopic........
LOL
I read the title and my first thought was:
"God I hope he's taking his foot off the gas before shifting from reverse to drive"