I'm a Nissan owner for the first time, after buying a 2000 Altima GXE.  The  
re is an awful groaning/grinding noise coming from at least one of the
stock plastic wheelcovers (aka "hubcaps").  The place where I bought the
car tried lubricating the inside of the cover, but this did little to solve
the problem.  I know it's the cover (as opposed to mechanical driveline
parts) because when I take the covers off, no noise.

Is this common among Altimas?  Any advice?