First of all let me say I'm not familiar with your equipment. I would assume that the PMD is powered from the USB port. USB ports supply approx. .5 amps per socket, their are 2 sockets in a pair. The PMD is probably drawing a full .5 amp or more, as hard drives use a lot of power. The iPhone draws about .5 amps also. So you may be drawing the max those USB ports can put out. I suggest if you have another pair of USB sockets, to move the iPhone to the other pair of sockets. If you only have a one pair of USB sockets, try a powred hub for the PMD. The clicking noise makes me think it's starved for current. Another words, it can't put out enough power for both at the same time. Most other USB devices don't use much current or none at all from the USB ports. If the PMD is powered from another source, wall-wart, never mind. LOL