Is it "No one will notice but you and me" or "no one will notice but you and I" ?
This hinges on whether the word "but" is interpreted as a preposition or a conjunction.
If "but" were a conjunction, then the sentence is a shortening of:
No one will notice, but you and I will notice.
Consider the similar case of "He works harder than I." as a shortening of "He works harder than I work." Under this interpretation, "I" is preferable to "me".
On the other hand, if "but" were a preposition, then "you and me" is clearly an object. Perhaps this interpretation is more natural to most. The use of "but" as a preposition is widely accepted by dictionaries (see for instance wiktionary).
In light of this, I would personally prefer the construction "you and me" because it seems more modern and is less likely to attract attention. However, I would not consider either construction wrong. Use whichever is more appropriate for the context.
These Google Ngrams seem to indicate that most people think that 'it' is
No one but us will ...
No one but we will ....
These Ngrams, for 'know but you and me'; 'know but you and I' might be interpreted as showing that
'No one will know but you and me'
is much preferred to
'No one will know but you and I'.
One could extrapolate further to the situation with OP's examples.