Thanks for the recommendation. I went ahead and ordered one of these because the volume level on the head unit doesn't match the OEM deck's volume out...so when I turn up the volume I can only turn it up to volume level 11 or 12 before distortion, whereas I could turn it up to 20 or 21 in my old car. This should solve that issue.
I'm not so optimistic that it will solve the alternator hum, though. Any other places to check while I've got everything apart again installing the converter?