Occasional Slowdowns?

Lately I've been playing Mario Galaxy and I've been noticing that I'll occasionally slow down lower than 100% for a few seconds then it will speed back up. Any ideas how to fix this? Or is this normal? It happens at the beginning of every level as I'm flying in, as well as a bunch of other places. Also - is there any way to see the speed % while in full screen? Thanks.

Edit: It also happens in Mario Galaxy when I'm picking up a bunch of starbits at one time. Thanks.