When you say that something is `noticeable', what you mean is that it is apparent. In other words, it is obvious, it can be seen or `noticed' by others.

There is a noticeable improvement in the champion's backhand.

What is noticeable is that the two brothers just can't stand each other.

Anything or anyone that is important or interesting is `notable'. The word is normally used with people who are well known. It can also be used to refer to their impressive accomplishments. Winning the Grand Slam twice is one of his notable achievements. `Notables' is normally used to refer to important or powerful people. Many of the local notables decided to stay away from the event.