Tranny problem ( i think)

Ok guys I need your advice again. The table is turned.
I seem to be hearing this noise coming fron the right under side of my engine on the 81 LTD 1000 and its ugly and feels ugly. I am thinking something is wrong with the 1st gear section. Let me give yall a description. I start the bike and then I start to move off and then there is this clank like my center stand dropped and came back up, but it didn't. this happens at slow speeds only when starting off and sometimes I won't hear it when going faster on 1st, but its there.. the noise! I also think it was warning me long ago because when I would go riding I would release the clutch to listen for noises and there would be this noise like " whrumph, whrumph" like an oscilating noise so I thought it would of been the wheel bearings so I got new ones but I didn't install them yet. I put the bike on the center stand to feel this noise and it spins freely. I also feel this noise in the brake pedal and I don't have to apply brakes to feel it.
Anyone have any ideas, I am about to open my oil pan to check the pump screen. Anythingelse I would need to look for? Do you need anymore info?

No metal in oil the last time I changed it!

I would check the output shaft bearing first, all you have to do to get access to check it is remove the sprocket cover. If that bearing is good, then I'd check the clutch side.

I have the oil pan off now and when I turn the rear wheel it has like this amount of play before the gear touches the next. I would say this play would be like5 -10 degrees rotational play in a whole circle. The gears look fine, no out of the ordinary scratches. Would my wheel bearings also cause this, even though they dont have much side to side play and the wheel rolls smoothly of the ground?. I will check the bearing as you told me steell but give me more suggestions on whatelse to check while I am down there (damm that sounded weird)

The wheel bearings shouldn't have "any" side play. Easiest way to check bearings is turn them slowly by hand and feel for roughness.
If a bearing does not feel absolutely smooth as you rotate it, then it's bad.

mine has this little side play like a small tick of a play, rocking it side to side.

the gear "dogs" will allow the wheel to rotate at least 5 to 10 degrees. thats normal

Yeah I just realised that btchalice, now that I remember the bike can go forward and back while in 1st gear. I totally forgot.

OK So I guess there is nothing wrong with the gears, since there isn't like a 1 sided wear pattern, scratches, breaks and the shafts they run on, I don't see any movement for now, but I will check that at the sprocket cover Steell. As for the wheel bearings I will have to do later or another day, since the mid day sun is so hot and my skin pores are blocked by a sun burn I got in St.Lucia, so they just turn into these small water bumps