Is it a sin to feel let down by God?

Questions about whether it’s a sin to feel let down by God and whether it would be easier to have a personal relationship with a rock than with a God who hasn’t spoken in over 2,000 years.  

• Is it a sin to feel let down by God?
• It would be easier to have a personal relationship with a rock than with a God who hasn’t actually spoken in over 2,000 years. What kind of God would be that way?