Fred 
2006 Nissan Sentra Sedan 1.8 S 4dr Sedan (1.8L 4cyl 5M)
5th Gear Whine
 My wife and I really liked the Sentra when we test drove it.  It was small (I am 6'2 and 250 lbs) but was comfortable enough for me to drive.  There is no room in the back seat behind me when I am driving, but we are getting 38 mpg on the highway, and 33 - 34 combined and fuel efficiency was our goal.  One thing that really disturbed me was the engine noise produced at 60 - 65 mph.  There is a very audible whine that sounds a lot like electrical feedback.  We had the transmission replaced, but the noise never went away.  The dealership claimed that it was just part of the 5 speed Sentra.  To their credit, I test drove another Sentra yesterday and it whined too.  It may not bother you, but check