My one also has crankling sound. I found out that it’s something to do with WIFI. If i use wifi heavily such as downloading files or watching streaming video, ezpad makes hissing sound. I think noise shield is not enough for wireless chip and antenna. Maybe Power management in mainboard while using wifi is problem. But in the point that other tablets using kinda chinese style reference mainboard have no problem, So i think hissing sound is only related to noise shield. Anyway, if i have time, i will open ezpad and find out way to install noise shield.