96 200sx, im adjusting the valves and hoping this fixs the issue
http://www.nissanforums.com/b14-95-99-chassis/89586-alot-valve-train-noise-oil-change.html
I'm not one to copy and paste these on every reply, but as I was looking at drawings of your engine to figure out what you have, I came across this, and it is something I would have mentioned myself. My engine sounds like a sewing machine, it is the timing belt tensioner, I replaced it twice, still makes that same noise, it is noisy, but runs perfect, 230,000 miles, I have another one just a hair quieter with 250,000 miles on it, the tranny went out on it, but as soon as I find another one, it will be back on the road. Anyway, try the heavier oil, Synthetic works great on newer engines, but for some reason, it doesn't do too good on old ones. Check it out. You might find the valve specs here too.