rear speaker not working occasionally :-(

[hkka]

My 172's rear right side speaker not working occasionally. It is like work for 3 sec and then gone for 2 seconds.

What would be the most common reason? Loose wire connection?
Can the speaker itself got problem??

 

[Tigger]

Check the connection to the speaker maybe?

 

[Redler]

Are they the standard size (13cm) because i put (17cm) in the front and found if tightened to much they would occasionally cut out due to them having a loose connection