Brad, some components tie chassis ground and board ground together and others don't. I have always thought that they should be seperate and isolated, as this provides some type of shielding to the circuitry courtesy of the metal case. Obviously, this is not how all design engineers or builders think, so we are stuck with no uniform code for production.
Some simple hints that you are probably already doing or know of:
1) Keep your interconnects well away from power cords / transformers
2) If you can't avoid having interconnects run near power cords, try to have them cross at right angles. Having one cord run parallel with the other increases inductance i.e. "induces" stray magnetic fields and voltages into the signal lines
3) Remove and clean all connectors on a somewhat regular basis. Connections do oxidize even if you think that they are "secure" and "tight". JJ from AA has commented on this and stated that he can MEASURE distortion on a connection that has remained intact for 30 days or more. Simply removing and plugging a cable back into the same jack can lower distortion.
4) Do not place or anchor power cords along the vertical risers on metal racks.
Hope this helps... Sean