From the front-Enders perspective the J was quieter as we were all issued with ANR headsets! It might have been marginally noisier down in the stalls but there was less vibration, possibly due to the slightly more modern synchrophaser.
I recall one occasion as a co trying to sort the imprest paperwork down the back of a K, I selected the seating forward of the landing gear, in line with the props, put my folder down as I sat, by the time I had settled and reached for it it had vibrated onto the floor. I placed it back on the seat and watched it as it immediately vibrated off again. I don’t recall whether the props were in need of a re-synchronising, which they did seem to do regularly. In the J in the unlikely event of needing one you just reset the FADECs as I recall.