Are silent prayers heard? Growing up in the church, silent prayers are pretty much part of how I pray.  However, challenging assumptions, I'm curious to know how biblical this is.

Every prayer I've found in the Bible is spoken out loud.  So, what is the biblical basis for praying silently?  Is there any biblical indication that praying silently is just as effective and beneficial as praying out loud?
Both Genesis 6:5 and 1 Chronicles 28:9 (and myriad other passages) indicate God can understand our thoughts.

So, can God "hear" our silent prayers? Of course!

Is it better to pray out loud than to pray silently? Since there seem to be no instances in the Bible of a recorded silent prayer (other than in the Epistles where Paul writes how he prays for people, or even writes a prayer to the Lord) - I don't think you could make the argument that praying silently is "better" than praying out loud.

However, I also think that since God looks at our motives, and we are told to "pray in secret", that silent prayers are going to be as effective if they are of the same heart as our aloud ones.