How about Service Bulletin 06-046?
Rattle or Buzz from Rear of Vehicle, Exhaust Tips Misaligned with Bumper
http://www.alldata.com/tsb/Honda/115...046/60461.html
It applies to all 2006 Accord V6, but you have a 2005 HAH. Maybe...
Also, I hope that disconnecting the rear speakers does not affect the ANC (Active/Auto Noise Cancellation) - though a post indicates the front speakers are involved with ANC.
http://www.greenhybrid.com/discuss/l...oise.8055.html