I have been noticing lately that my 98 malibu has a thumping noise coming from the driver side tire. It'* almost like a flat tire noise or when your on the freeway and driving over the reflectors in between the white lines. I don't usually notice any noise when the wheel is being powered ( by powered I mean foot on gas petel ). It'* more so when I take my foot off the gas and basically coasting. Most predominant when costing at 30 mph. Anyone have any ideas or a list of how to diagnose this issue?

You could try to swap tires from front to rear for example and see if the sound also moves.
It could be the tire, but often on FWD cars, the wheel bearing/hub, could be suspect as well.
While mine was on the lift, it was easy to tell with a auto stethoscope placed on the rear of the hub/plate, with wheels was spinning at 1800rpm, it was the front passenger side hub that was noisy, and required replacement.

Well I also noticed a few other things to. It don't really sound like a tire issue to me... because the sound goes away when accelerating. Also when the noise is the most predominant I notice the steering wheel turns to the left. Not drastically though. More like half an inch turn at a time. I been working alot so havnt had time to rotate the tire but I will check that maybe this weekend.

I had a similar issue awhile back, turned out to be a loose wheel weight.

I've experienced this sound before, on my Vette. Sound came from the left rear, and ONLY when I lifted my foot from the accelerator at low speeds. It was a bad U-joint in the rear half-shaft.

Your'* could be the CV-joint or Tri-Pot joint. When your foot is on the accel, it takes up the slack in the worn joint and the noise disappears. Letting off (at low speeds) allows it to slack off and make noise.