Finding the source of this noise in this Bosch dryer was tricky. Judging by the sound, the noise had to originate from either the motor or the blower wheel. The problem turned out to be the blower wheel. The noise was only heard in a heated dryer cycle. Apparently the heated air would deform the plastic blower wheel just enough to make it contact the blower housing while rotating.

Here are the part links to the drum rollers and blower wheel that I used to fix this dryer:

Drum rollers ==> http://www.repairclinic.com/PartDetail/Drum-Roller/422200/1105531

Blower wheel ==> http://www.repairclinic.com/PartDetail/Blower-Wheel/491640/1107382