I have a 97 Maxima SE with relatively low mileage (about 80k).  I have
had zero problems with it the last 10 years and it has had regular oil
changes and maintenance.  Suddenly over the last month it has developed
two different noise problems.  The dealer cannot find the cause of
either.

One is a grinding noise after startup that lasts about 2-3 minutes and
until the car warms up.  Then the car runs fine and the engine is quiet
as always.  First the mechanic suspected the known starter problem, but
given the noise is not extremely loud and stays around for a few
minutes we agreed it wasn't the problem.  The noise cannot be noticed
outside the vehicle or when the hood is up.  It is heard more clearly
inside and the vibrations can also be felt with the gas pedal.  The
mechanic also checked the oil level and said it was fine.

The second problem is a thud/flapping noise coming from the right wheel
area.  It happens at low speeds, going over some bumps and rough road.
It comes and goes so it is difficult to pin down.  The car does not
pull at all and other than the noise, there is no steering or control
issue.  The mechanic had the car up and checked underneath and cannot
find a cause (said wheel, axle, suspension, etc. seem fine).  I
discovered that some of the screws holding the various plastic panels
underneath were loose or gone and replaced those thinking they were the
cause of the noise but it didn't help.  The mechanic noticed a couple
of loose rings around the exhaust system pipe, but they are more in the
middle of the car and make a different noise.

Has anyone experienced either of these problems?  Regarding the first,
could it be oil pump related or simply something loose that shakes
until metal expands? (the engine mounts are ok.) As to the wheel noise,
can it bushings?  Something wrong with the tire and the metal belts?

Thanks,

Ron