...How loud are they?

Staintune pipes decibel range will vary depending on the bike, and whether or not you use the sound restrictors. On average, as a general rule, the pipes run in the low 90's with the restrictors in place and just over 100 with the restrictors removed. 

This is a general rule of thumb and can vary  depending on the individual model. A Ducati twin will definitely be more heart and ear pounding than an inline four BMW. The design of the engine can vary the number a few decibels +/-. With the restrictor in place you will get an exhaust note that is just slightly louder than the stock muffler. It will be throatier under acceleration and deceleration and only the slightest bit louder under steady throttle. 

Think of it as a shotgun choke which reduces the diameter of the exhaust exit. It has only a very small effect on performance when installed, and its main function is to reduce the exhaust note to a very pleasing level. 

STAINTUNE pipes are actually one of the quietest aftermarket exhausts you can buy. Even with the sound restrictors removed, they still come in a few decibels less than almost all other aftermarkets pipes.

With the restrictor removed you are now in full "Sport-Pipe" mode and the bike will be louder under all conditions (idle, acceleration and deceleration). A better way to put this whole picture in perspective is to determine how well you like your neighbors. With the restrictors in place you can attend the summer parties down the street. With the restrictors removed you can pretty much count on not getting an invitation in the mail.

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