Annoying notifications

My Droid Turbo 2 keeps beeping a notification sound but does not indicate the reason.  I suspect the 50 or so beeps I get are telling me I have received e-mail.  How can I turn that off, but keep the other notifications active?  Is there a way to apply individual sounds for different types of notice as one can do with special ring tones for certain callers?  How do I empty my cache to avoid battery drain?  Is this accomplished by clicking on the small square at the rt bottom and individually closing each recently used app or is there a shorter way or a way to have the cache cleared automatically each time an app is closed?

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