Hmmm...
Not sure, but check the easy stuff first. I'd open the plate on the floorboard of the back seats and check the coupler/bushings. You could also check the ones under the shifter and the one just benind it.
Has the feel of your clutch changed at all? Does it still engage about an inch off of the floor as it should? If not could be a clutch cable out of adjustment although I think these usual symptoms are a grinding 1st and reverse. Short of this I'd think the transmission might be the source.
Ryan