I must be lucky for once (it's about DAMN TIME!) 
We have TV/Phone/Net bundling and the
modem for my shack sits at MOST two-three
feet from mt PROII, K2, and TS-940S.....and just
under 4 feet from my venerable A "ARRIS
I get zero noise in my receivers and no
TVI, RFI, or phone interference.
This modem is labeled "ARRIS". No Wall Wart
with this one, it runs off of 120vac and the plug to
the modem is one of those "universalinternational" jobs.
Interestingly, it has a light on it labeled "Battery" so
must be have built in UPS. Do most Cable Mobems have this?
Actually, there are two lights. One labeled "Battery 1 and Batter 2"
but "Battery 2" is never on.
Well I've been working now for 20 minutes with the
the AC line unplugged and no difference in receiver noise
on the few bands I've checked, and Net and Phone
service is working. Interesting. I might take the lid off this
one and see what kind of battery it uses
I used to think Murphy lived in my shack
for periods of time, that's how many and
varied complaints I received or problems
encountered!
Guess a dodged a bullet with this modem business.
(Still gonna keep my head down though)

Good luck with your modem difficulties.
73,, Ken AD6KA