I recently took a sound meter to measure DB's at a local auto cross here. Many tracks DO have a DB limit, which seems to vary with the day of the week, time of the day and the particular event. Some tracks are more strict than others. The DB requirement seems to vary from 99 to 103 or so. I would ASSUME they all take the measurements at about 50 feet? Typically at a turn on the track somewhere. So, if you know what turn and where the sound meter is you could adjust throttle opening or turn your side pipe exit port to face away. Some car's do have an adjustable exit tip on the sidepipe specifically for this purpose. I may modify my side pipes in such a way.
Where was I? Oh yeah, so I took some DB readings at the START line as well as a straight section "at speed". The start line was consistently higher DB. Plenty cars exceeding 103 DB on the start, 105, 106. Surprisingly "at speed" showed a significant drop in DB, 5 to 10 points.
My ERA idles at 106 as read from the cockpit with me sitting in the drivers seat. I ALWAYS wear ear plugs, everytime, even for a short trip. I already wear two hearing aids, I'm just trying to save what I got left.
Because this is becoming more and more of an issue (in particular California) there are some ongoing studies as to what works and what doesn't. Glass packs don't work, period (that would essentially be side pipes). Borla and many other after market exahust systems don't work. The list of systems that don't work is long, the list of systems that do work is short. On the short list is Spiral Turbo inserts.
When I was talking to the Spiral Turbo folks and told them I had an FE, I could hear them groan. Apparently the FE engines are among the toughest to get the DB down on.
http://www.spiralturbobaffles.com/index.html