The key to this whole thing is cable channel 18, like I said his 2M signals are getting into the cable. You can't do anything about it and neither can he, that's the cable company's responsibility to find and plug the leak. If he's getting in cable signals are getting out over the air so the two of you should approach the cable provider on the matter. You may be faced with an I don't care attitude, profound ignorance bordering on stupidity or you may get lucky but once you've notified them the ball is in their court, you have done your bit and the blood is on their hands, not yours.
As for the scanner interference the deal is to filter out the 2M signals. He can help you with that, a simple coaxial quarter wave open stub connected to the line with a T connector worked for me before I was a ham and had that very same problem only with a different VHF band. If that doesn't fix it look toward a tunable notch filter.
He can use any mode on 2M and FM is but one of them so there are quite a few reasons why you're not hearing him clearly. Those modem tones tell me he uses digital AX25 packet mode at 2600bd, one of my personal favorites. (On 70cM 9600bd is permitted) While you're there maybe you can ask him if he's seen me on the BBS, if he posts bulletins to @WW I just may know him. If it's ARPS that's a different use for packet I'm familiar with but don't presently use. The references to video may be SSTV permitted on all bands or fast scan ATV on 70cM being hams use a 2M voice channel to coordinate on 70cM. Here's a neat trick, you can receive ATV by using a TV in cable mode connected to an antenna, I believe on channels 58 and 60 if I remember how I did it some years ago.
Anyway stop yapping about it and go see the guy and get some help with your problem. Git goin' now, I'm awfully curious to see how it all works out.