Sensor Dust Anguish
Is this the only zoom you own? If not try it with a different zoom. If the problem persists then I would assume that the mirror box is the issue. If it goes away, I would assume you still have a problem with the lens.
In any case the previous posters cleaning suggestions should work well.
|.....the ROYAL LOTUS 2017/08/25-NEW YORK..... by Chiwat|
from Wild flowers
|Coffee and Mango cake by clicker88|
from Another cup of coffee