Disco 1 rumble under load

I have a 1998 Disco 1 TDI 300 auto. I have just had it's MOT and needed to clean up the handbrake drum so removed the rear prop shaft to do this. Pretty sure I marked the positions correctly at both ends. At the same time I replaced the rubber doughnut linking to the rear diff, with a genuine Land Rover replacement. Since then I have this heavy rumble under load and at low speeds. It seems to go away at higher speeds and when not under load. Does anyone have any thoughts as to what this might be. Are they related or is this coincidence? Any help would be greatly appreciated.

you wouldnt have needed to mark anything up with prop with dough nut,which of the two ways prop bolts to flange on hand brake drum makes no difference neither does the three ways on coupling or splines on slide as long as no simple error ,or worn coupling /uj

Thanks, James. I thought I might have to mark it to keep it in balance. Any thoughts on the noise or do you think it is unrelated?

Did you grease the UJ and prop splines after refitting?