On a 1998 Subaru Legacy station wagon (not the Outback) running stock tires and suspension, with a 5-speed manual transmission:  I've been getting a vibration/droning at around 70mph +/-  3 or 4 mph.  The problem occurs in gear and out of gear.  A knowledgeable relative suggested it could be a warped or damaged rim that might have evaded tire replacement/balancing a year ago.  My wife was in a fender-bender a year and a half ago that required some front-end parts replacement along with a blown front tire. 
  
  
  
The dealer couldn't find the cause of this 18-month old problem.  Any suggestions?