Agreed, a lamp or psu issue would affect the ENTIRE image, there is no way a lamp flicker can be localized to one area. It has to be processor or DLP issue. You should be able to confirm by looking carefully at the area that is affected. Is the area regular in shape, defined by the pixels? Or is it without definition, nebulous?
Oh, and in the future, be careful with the canned air. Most DLP projectors do NOT have any filters and blasting with canned air can drive dust into the imaging chamber as you experienced, It isn't that difficult to clean, but it does require opening the projector to do it.