My magnaflows really aren't loud at all. They have a nice drone at low rpms and quiet down at higher rpms which is good if you do a lot of highway or long distance driving from a noise standpoint.
My understanding is the magnapacks are "resonators" essentially straight pipes with a small chamber to circulate the exhaust and cut out some of the noise you'd get with straight pipes. The mufflers have steel wool around the flow path to dampen the sound. Packs are louder than the mufflers.
Magnaflows will outperform flowmasters any day that is an indisputable fact.
I'm telling you, check out the pypes website before you buy, They outperform flowmasters and dynomax mufflers.