That high-pitch sound, from what I understand, is normal. If the filter is taking care of it, then everything should be OK. Analog modems only use up to 4 kHz, the human ear can hear up to 23 kHz. High-pitched sounds shouldn't be interfering with the modem. If the high pitch noise was interfering, your test calls wouldn't work either. Try 10 or 20 test calls and see what happens. Do they work? If they don't consistently work then you have a phone line, phone, DSL modem, or filter issue. If it works well enough for the test call, the daily should be fine from a modem's perspective. Considering people with Turbonet cards are also suddenly having problems, I don't think it's a modem issue.