Canon BJC-6000 strange behaviour positioning paper

Hello,

My Canon BJC-6000 printer is having a strange behaviour lately, I am
sure it never did it before.

Its normal when I turn it on , it makes lots of noise because i guess
it is like cleaning the heads of the ink catridge, this takes long
time and then it stops.

The problem comes as soon as I enter in the back feeder just one
single sheet of paper it starts again making lots of noise.

Sometimes it feeds the the single sheet of paper and moves it inside
for 1/3 and back and forth in and out for at least 2 times most 3
times.

Some times it does this also when I send the printing from word.

the it finally prints.

Why it does this? How can I avoid this? I am sure it didnt use to do
this before.

Thanks,

Mario