Modem drop-out from 6pm till 7:30pm

Recently I changed ISPs to a new company and my modem (I believe netcomm) died (all lights constantly turning on/off).
I purchased a Cisco Linksys and the net appeared to work fine for the whole day until around 6pm where it lost connection -- it eventually reconnected and when it kept happening I switched it out with the retailer for a new modem under warranty (D-Link this time) thinking that would solve my issue. However, I still face the problem and it appears the time for the modem not connecting properly is increasing (7pm last night, 7:30pm tonight.. Although both nights total around 70 minutes total offline time).

Both the Cisco and the D-Link the modems act in the following manner: The power light, Ethernet to PC and DSL lights are instantly green on boot during the down-time seconds after the Internet light flashes green where upon the modem restarts and within a matter of 3 seconds the sequence resumes.

I can think of two particular things that could be causing this -- Both of the new modems have been connected to them although not my original one (but, that acted in a completed different manner). A Linksys ATA adapter for Voip has been used (and since stored away because the drop-outs were to frustrating to rely on a net phone service) and a Power Guard surge protector (at the advice of a tech support place to protect any modems that I have connected to the phone line).
The removal of the Voip unit made the ISP's plan a waste of money so we changed back.

At one point our phone line outside the house was corroded and coincidently enough it was around when my original modem died (the original person who fixed it used heavy duty tape to fix the line, but, since then proper fixtures have been put into place -- So I've been told).

I probably haven't provided as much information as I can so feel free to ask questions -- Simple things I ignore could be an answer to you. Also, I don't believe there are any possible interferences from electrical devices (such as dimmers, night-lights, etc.. We don't have any and haven't had anything new installed since the problems started).

One other thing -- I'm thinking of getting another new modem under my warranty and isolating the power surge protector and the Voip unit (the latter as I said earlier is already done though).