Thanks, SafetyBob, I read that earlier and I really appreciate it. I think you may be right, as I think I'm close to cracking the case on this one. I was busy the last weeks and just yesterday, scanning C-41, I picked up on a pattern I hadn't noticed before.
The first 4-5 frames (i.e. the first of two cut negative strips in the scanner's neg holder) never appeared to have this line. So, in effect, the 1st, 3rd, etc. strips in a negative sleeve wouldn't have the line, but 2nd, 4th, etc. would. How strange! So I inspected closer on the negative with my own eye, I did see some scratching, but it was in a different place on the negative than the line was appearing on the scan. Clearly the scratches I was seeing weren't significant to the scanner or digital ICE.
With that, I decided to do a bit of testing. I would put the first strip in the second negative holder slot for the scanner, and wouldn't you know it, a line appeared! So, I decided to do the inverse, scanning the 2nd, 4th, etc. strips in the first slot...now no lines! I'm now scanning 1 strip at a time, in the first slot only, and haven't seen any scratch lines yet.
I've got some black and white to try out still too with this and I might want to go back to older negatives and re-check, but I'm pretty sure it is the scanner now. Which means, my negs aren't screwed up for darkroom printing! That is a huge sigh of relief for me. I'll keep you guys posted for any future tests I do if interested. I also want to once again thank everybody for their help and support with this very annoying issue and I do apologize if I came off harsh, I was just getting very frustrated with this.