The only thing fun about murmuring is saying it. Murmur. Murmur. Love it.
The reality of the word is that it's a verbal cancer. It destroys all who it infects. Murmuring is that condition of the heart that erupts in the mouth. It is a nasty condition which seeks to elevate personal preference, opinion and perspective above community health, respect for authority.
Murmuring is an ugly thing. Back before Blockbuster and Movie Gallery took VHS rentals mainstream, most communities had a mom and pop video rental store. Movie rentals were the next big thing. With Blockbuster's recent bankruptcy, we all realize we're living in a new world. Pre-internet, a few of these unscrupulous small shops would have a back room. It was where the "adult" videos were. That's how I envision murmuring. It's back room verbal porn. It's that nasty and unhealthy.
It got the Israelites in deep kaka with God.
Yet you would not go up, but rebelled against the command of the LORD your God. And you murmured in your tents and said, 'Because the LORD hated us He has brought us out of the land of Egypt, to give us into the hand of the Amorites, to destroy us. Where are we going up? Our brothers have made our hearts melt, saying, "The people are greater and taller than we. The cities are great and fortified up to heaven. And besides, we have seen the sons of the Anakim there."' (Deuteronomy 1.26-28)
Their murmuring de-spirited the people. It absolutely destroyed their focus and reliance upon God. In this case, they looked at the giants in the land rather than their God in heaven (who was bigger).
The Israelites were still regretting their ancestors' murmuring years later, as recorded in Psalm 106.24-27:
Then they despised the pleasant land, having no faith in his promise. They murmured in their tents, and did not obey the voice of the LORD. Therefore He raised His hand and swore to them that He would make them fall in the wilderness, and would make their offspring fall among the nations, scattering them among the lands.
We see a New Testament example of this same offense in John 6.41-43:
At this the Jews began to grumble about him because he said, "I am the bread that came down from heaven." They said, "Is this not Jesus, the son of Joseph, whose father and mother we know? How can he now say, 'I came down from heaven'?" "Stop grumbling among yourselves," Jesus answered.
As far as verbal sin goes, murmuring delights in being the undisputed king of back room conversations. It worships quiet corners. It thrives in the petri dish of dissatisfaction. Where murmuring can find a discontented heart, it can gradually move from the aorta to the mouth, where its contagion is spewed into the ears of susceptible victims.
The only cure is contentment.
Paul said that contentment was a learned state.
I have learned to be content whatever the circumstances. I know what it is to be in need, and I know what it is to have plenty. I have learned the secret of being content in any and every situation, whether well fed or hungry, whether living in plenty or in want. (Philippians 4.11-12)
It's a mental exercise of bringing your soul and heart to submission under God's love. What He has given you is sufficient. Period. Learn to be joyfully content where you are.
Murmuring is an insurrection against God's authority and any other established authority over you. If you don't seek contentment on your own, someone may have to take drastic steps to deal with the devastation that murmuring causes.
If you're prone to murmur, I'd find the closet piece of wood and nail that proclivity of yours to it. Crucify it there. New life will erupt in your soul when you kill murmuring and experience contentment.
And those who belong to Christ Jesus have crucified the flesh with its passions and desires. (Galatians 5.24)