While good advice in general, the fact is that a non-Apple branded SCSI disk drive will not stress out your internal PSU even if that drive is installed internally. My 4.5GB hard drive was actually used in servers years ago, not Macs. But my Mac handled it just fine internally. It was only when I maxed out the RAM and then added a power-hungry 040 accelerator AND an Ethernet card at the same time that I felt my PSU might be taxed. So at that point, I added a secondary PSU (you can also see that on my Flickr account). But I later found an old HD20SC enclosure for sale and I moved my hard drive to that. You could do the same. That way, you can use any drive you like. But again, if you don't plan to add an accelerator, go ahead and put whatever hard drive you like inside the SE/30. The PSU is more robust than you think. If you doubt me, pull the PSU and look at the specifications on the label of the PSU itself. It can handle it.

As to noise, you'll need to swap out the stock ELINA fan too. I replaced mine with a Silenx 60mm and my SE/30 is much quieter now.