My idea is that the numbers you're getting are both correct. The temperature at the probe is probably 34C, and the temperature at the internal sensor in the hard drive (where the SMART temperature function gets its data from) is probably 47C. 47C does not seem an unusual temperature for the D740x, which is supposedly one of the hotter drives around. Storage Review reports the temps for it as 20.5C over ambient*, and since you have it in a mobile rack, that probably increases the temps a bit. I don't think you should be too worried if 47C is your max temp-- if it's the idle temp, then I'd be a little worried. If you're worried that your temps are too high then your only options are to get aluminum mobile racks (if you aren't using them already) or add a fan (and that's never a good answer in the SPCR forums). I suppose that if you were feeling a little crazy you could cut chunks out of your current mobile racks in the hope that more direct access to circulating air might cool the drives down a bit. But, hey, man, that's just crazy.
* As reported in their Seagate Barracuda V review