I know that there are several accounts of people hearing what could have been explosives, but many others say the same, so really it's hearsay. That, plus it would have been difficult for thew government to install bombs in both towers without anyone noticing.
Saw your thread about 9/11. Your question was, why didn't anyone notice if there were explosives there.
Well, if you watch "loose change" documentary, they show a reporter talking about something that sounded like bombs going off...as well as many janitors/workers that were in the next building saying the same thing. They heard something go off one by one. I donno how true it is but that's what they showed.