chain jumping when in gear...

[glynblue2]

you state the rear wheel is tight is that your tight or tourque tight?remove the chain completely remove the rear wheel replace the rear wheel and re-torque do nothing else but this then you will have a starting point,if the movement is still there remove the rear wheel again and check everything,if you are sure its the wheel moving then it can be a number of things but visibly check everything first,then come back and let me know what you find?