What is the difference between Ikhfaa and ghunna?
Answer
We assume you are referring to the ikhfa' of the
saakinah. The ikhfa' of the saakinah is the process of hiding the , meaning it is neither said clearly nor is it merged in to the letter that follows it. The tongue gets close to the letter following the saakinah and while doing this, a ghunnah is produced from the nasal passage. The ghunnah is a nasalazation sound that comes from the nose, and is an inherent part of the and 
. The ghunnah accompanies the hiding of the
, so is a part of the procedure of making an ikhfa'. Please see: http://www.abouttajweed.com/the-noon-saakinah-and-tanween/hiding-ikhfa-rule-of-the-noon-saakinah-and-ta.html
and http://www.abouttajweed.com/the-ghunnah-and-its-ranks/the-ghunnah.html