No the 1100D is way better noise wise over the 350D, its very close to the 450D noise wise.
http://ghonis2.ho8.com/DSLRcomparison.html has all the data to prove and shots. If you leave the camera running live view and don't let it cool off before shooting of course there will be more noise. I would get a cooler box and i think you will be blown away with the results. I always use usb pc remote mode and never shoot with the camera its self, get your self a notebook and backyard eos
Have you tryed adjusting your iso ect?
I will say these camera's are the bomb and nothing come remotely close at the price bracket for astrophotography, they do however suck due to lack of features for normal photography by mid level and pro's, but hey what the hell do you expect for $300. These camera's are that good that these guys have spent god knows how much building a full blown TEC cooled astro cam out of them for resale
http://www.centralds.net/cam/?p=1687 . I'am also doing my own rip of there camera with a tec and cold finger, just check out the results.