Hey guys I have what I believe to be a THM200/C transmission.

When my car is a low speed or idling it makes a rattle noise that sounds like it is coming from the the area of the transmission/engine link. When I rev my engine it will go away, it is only there at low engine speeds/idle. I raised the idle speed and it stopped. My buddy says that it might be a cracked flywheel.

Comments? Suggestions?

Check your bellhousing bolts. Since they only require 30 or 40 lbs to tighten they do loosen off easily. If they are jack the engine and transmission up to realign then if needed and re torque the bolts. Your flywheel probably is not cracked and the noise is probably the flywheel flexing with the rotation of the motor. I have had this happen on two of my cars.

now is the flywheel flexing a thing that I could fix myself or would I have to take it to a shop?

no because the once the bellhousing bolts are tight then it will re-align the torque converter to be parallel with the crank and keep the flywheel from flexing.