Efficient Speed Stream modems tend to run hot. For maximum cooling they should be placed in a well ventilated area and placed on its side. It is also known that sometimes the models are shipped with the wrong AC/DC converter.
Modem revision 1.6 and earlier work better with the 15-18 v power supply. Revision 1.7 and the new ones with no rev # should work better with a 12 v power supply. In both cases, better means cooler. Rev 1.6 and earlier usually work with the 12 v PS, but sometimes get too hot to touch.
Standing the modem on its side is better as the regulator is on the right side of the board as viewed from the front.