I have a 1990 Nissan Maxima, not sure if it's a GXE or a SE, (how do you
tell?)
It has the standard 3.0 v6 engine, here is my problem/question(s):

I have checked with the manufactures specs about oil changes, which
recommended -
Changing oil every 3-5000 miles and Filter changes every other oil change.
I did do an oil and filter change back in April, (since the odometer counts
mileage at random, it's at 170K miles - but bad counting gears or rpm wire
only work intermittently, whatever... no worry I change oil by the month,
not the miles).
I did an oil-only no filter change in May (10-w30) and had been noticing a
slight air hiss or popping sound coming from under the car on the drivers
side, leading to about middle under the motor. I checked with a couple of
friends that work at Goodyear and they said it was normal sounds, but
I say if it's normal why did it only start just recently?

My BIG Question is this.
I have what sounds like a valve noise coming from about dead center to the
rear top side of the top of the motor. Mostly sounds like there isn't enough
oil getting up to the parts in the engine. When I first start/spin the
motor, it starts up fine. There are about 3-4 different knocking, clicking
noises that I hear, and 2 of them go away after about 20-45 seconds of
running. The last noise concerns me since it does not go away and gets
louder at times. Some of the time it will go away at higher RPMs, but I am
not sure I am just loosing the sound because of other higher noise. The OIL
LIGHT starts to blink about 20 miles in to a country - non-highway drive.
Some times the light will stay on, but I have the oil dead set on
Normal-Full. When I first noticed this noise, I checked the engine and it
had about 1/2 - 3/4 qt of to much oil, so I drained it and filled it
correctly. The oil light some times flickers or is steady at start up and
goes out which does not worry me. It's when the oil light come back on in
20-30 minutes that make me think it's a bad oil pump, a sticking valve, or
some other thing that I have no clue about.

Also, I am looking for a cheap place to find replacements for my window
regulators, high side power steering line, Front Fascia (bumper cover), and
pitted windshield (that I may let someone else do).

Any comments, or advice, including comic relief are welcome, please post
your reply as soon as possible, I don't want to ruin this engine or it's
driving life.