The bottom fan sounds like its vibrating against something. 120's are typically quite even at full speed. You can press on the fan casing and see if it quiets up. If so get some silicon washers/spacers to put between the fan and the case. The screws would go thru them to give you an idea.
the 3 wire fan into the 4 pin adapter should run that fan at 100% just like plugging it into a molex but the adapter throws a curve into this. You might need to remove the 3rd wire (fan speed) so as not to confuse the motherbd. I'm thining one of the adapters would not have this wire anyway so check both 4pin ends of that adapter you have and use that one for the 3wire fan.