I would say its just the heat, DSLR just suck in high temps without cooling hence why cds make astro cooled models. You could try a cooler box, really though dslr's weren't made for the job, in winter you have temp's on your side though. Test it by putting it in the refrigerator and see for your self
Best solution go with a tec ccd or a tec cooled dslr but i'am sure the dslr crowed will be up in arms over this comment haha.
Anyhow if the refrigerator test fails then send it back as it could be a bad ground somewhere or emf issue, though i have only had this happen once with a modded 1100d i did.