Amp "pop" - need help

just purchased a McCormack DNA-1 Deluxe. While the sound quality is greatly improved - better stereo separation, deeper bass, less harsh highs, improved dynamics - I have noticed the amp gets quite hot. After just a few hours the heat sinks are hot enough to be quite uncomfortable to the touch. Worse, though, the amp makes a popping noise as it heats up. Sounds a bit like metal expansion. . .the wife says it sounds like the last kernel of corn popping in the microwave.
Not sure if this is an issue but it sure is a big change over the previous amp that would run all day without overheating.

Any ideas?