If this thread is supposed to be about the DTT900 after all, mine is dated January, 2008, its serial number is 801SHNG058231, and I can't detect any audio faults with it.
If this thread is supposed to be about the DTT901, then nevermind.
EDIT: Sorry, I misread tkrhdtv's "don't you mean the DTT901?" in the third post
as a correction of the original basenote (which was doubly careless of me in retrospect, as tkrhdtv started this thread and was the poster of the basenote, plus it questioned "DTT990" [as in Rammitinski's post] rather than "DTT900" [as in the basenote]). It was a correction of Rammitinski's typo of "DTT990" for "DTT901." As Avio has since posted, this thread was started about the DTT900, and the DTT901 came up in subsequent conversation.
Since Avio has already quoted my original text, I'm leaving it as it is and adding this edit below it instead.
OK, then, forget the "if/supposed" parts; my DTT900 is dated January, 2008, has the serial number given above, and has exhibited neither the chirp nor any greater sibilance than I get without it.