Be careful if you're going to use the phenolic spacer. It's OK to torque the long center bolts to spec but the tabs on either end of the upper intake are not strong at all. Without the rigid aluminum lower to back it up, one or both tabs can crack away from upper.When using the spacer, it is better to snug up the two short bolts (front and rear) lightly and not go to full torque. Sealer on the gaskets should take care of any potential leaks.
Noise could be throttle valve, IAC or vacuum leak. Check for upper intake cracking as noted above - also possible before adding the spacer. Check the PCV on the back of the lower. Grommet can get hardened with age and leak.