I had the problem 3 weeks ago, at first I thought it was only temporary. All of a sudden, the speaker sound was gone. Just send it to ASUS Service Centre if you have that crackling sound, you'll get back your N7 in a week time like I did.

I'm using Nexus 7c with Hotlink SKMM simpack, only RM25 for 1GB (Very cheap woo). The only drawback is everytime I get disconnected from the internet I need to click on the continue link. The good thing about this is at least my bandwitdh quota doesn't get hijacked by some apps running on the background. Another good thing about Maxis Hotlink the top up is done online, no need to use SMS to top up (Stock Nexus 7c can't install any SMS apps based on my experience).