why are there so many loose bolts on my Cadillac engine?

Concerns about "loose bolts everywhere" would be alarming on a brand new, never serviced vehicle with less than 10,000 miles. On an 11 year old vehicle with unknown service repair history -- it's best to focus on your concerns rather than the indication of loose bolts found. Also, torque specifications for fasteners will vary -- make sure as you reassemble you are using a torque wrench and following manufacturer specifications. It is far more concerning about the internal engine noise -- certainly, repair what you find to be suspect, but you could still have a "rod knock" once you get the engine back together again. It's hard to know much without tear down and inspection, but your dealer technician would have some "pattern failure" experience and first hand knowledge of these engines that may prove to be accurate at some point.