Did you get the package from Bull or UCLA?
If you're on 5L, you can install from the expansion pack a version that doesn't require a separate prngd.
If not, prngd should have a config file somewhere that list commands that it uses to gather entropy. If you can identify the particular processor hog, you can comment it out. The "after a few days" part is strange, though. Usually, processes that will causes problems show up immediately.
Rod Knowlton
IBM Certified Advanced Technical Expert pSeries and AIX 5L
CompTIA Linux+
CompTIA Security+