There is a spot you can see even without PS
but I understand why you miss it - it is not easy to see by fleeting glance.
To prevent cases like that I'd recommend you yo use Equalize (Image - Adjustments) option at PS
. Do not neglect this option at the future - always good to check your picture. It will help you to clearly see spots like that and at least will give you the good signal if you need to clean your matrix (if the same spot is at the other pics it is looks as your matrix is a bit dirty).