Omitting 'e' in lovable vs likeable

Hi,

I have a question related to spelling. Why do we sometimes remove 'e' while adding 'able' suffix and sometimes leave it?

noticeable ('e' present)

changeable (as above)

likeable (as well)

but: lovable, unbelievable, curable, valuable

Is there any rule that applies here?

Greetings to all! (especially to CalifJim or Mr. Micawber if they are still here)