For the 2U I really prefer the "A" series backplane but the SAS2 backplanes work great too. Unlike the 4Us you don't have to worry about getting an "old" SAS-1 expander because, AFAIK, SM never built a SAS1 expander backplane for their 2U chassis.
Noise is no more or less of a problem than you find with the 3U/4U chassis. Same PSU modules as used in the 3u/4u chassis so the issues are the same - if you get the right PSI (920SQ or 720P/510P) you can manage the PSU noise. If you get the non-platinum PSUs they scream like a jet.
Backplane fans are same story too. Watch for older revision chassis that has 3-pin fans. No love there. But with the PWM model and good fan speed control from your MB you can slow them down to tolerable noise levels and still maintain cool operation. Remember that SM designed the fans expecting to run 24x hot 15k SAS drives in the backplane - you probably won't be doing that so you have lots of headroom to slow the fans and still cool the disks.