HDR always turns out blurry

I have my C3 programmed this way:

1. AV at 5.6--sometimes I use Quick select and change it to f8

2. iso 100

3. three shot bracketing at 1 1/3 increments

4. one shot

5.  high speed continuous

I then use the 2 sec delay to fire the shutter. I've never had a blur problem. I often use a tripod but have done it hand held if the light is decent. Of course, I wouldn't use the 2 sec delay hand held.

I've processed with DPP and Photomatix. On occasion I've had some lining up problems with DPP, but never with Photomatix. I'm also a bit lazy and never lock up the mirror.

I'm  using a 7D