My 98 Altima makes an increasingly loud rattling noise when it is cold, and
only upon accelerating in gear (won't do in park while revving engine).
When you accelerate, it sounds like a diesel engine until the engine is
warm.  When the car is driven a short distance and restarted, the idle
revs really high, kicks down, revs high again and eventually finds a
normal speed.  Not sure if the two are related.  Nissan dealer who heard
the noise last year told me it is "normal" even though it never made that
noise when new.  3 years ago they replaced the idle pulley and that seemed
to help, they say that is not the problem.  I am concerned that this
indicates something about to break on me. Any ideas?