User blog comment:Xilinoc/Ch. 545 - Blue Stripes/@comment-4822693-20130709222211/@comment-11051098-20130710212207

Ichigo became stronger than Aizen after his Dangai training. If it's true that his reiatsu far surpassed that of Aizen, maybe it was so high that his friends didn't feel it when he arrived in Karakura Town to confront Aizen.

Aizen stated that he had to lower his reiatsu to "a level that normal people could feel" or something like that. I don't know if that also counted after the Hogyôku started to transform him. But since Ichigo can't control his reiatsu, he would probably be unable to lower his reiatsu anyway, hence why his friends couldn't feel "anything" from him.