The sound did indeed lack punch in this one. There are numerous possible explainations, as were listed in the first page of this comments section (which was about as much as I could be bothered to read) but none the less, this is best explained and hoped for as an anomoly.
Maybe his tonsils are swelling, on their way to becoming a frightening new mutant life-form.
Maybe he's been replaced with a more corporately-compliant doppleganger or impressioner.
Maybe he's bored of the whole thing.
Hmmm, actually, this conjecture business is fun.
Maybe he's...