Images have black vignette effect

Question

Canon EOS Rebel XT. This happens mostly with indoor images; noticed the problem after I changed the setting to RAW, but think I have changed it back to L now but I still get the black feathered vignette effect around images. I hate it. Husband has several filters on the lens. Everything comes out too dark. Camera is 3 1/2 years old and has always worked great before this.