The phone rings but no msg is left.

they call and hang up

Call every night but noone on the other end.

same here
they call every nite at around the same time and hang up
This nite there was a screeching sound sort of like when you call a fax number.

I received a call from this number for three days in a row and every time I answer, they hang up.  I called the number back and of course my only choice from the automated menu was to speak with the operator and imagine this....the operator is automated also.  So I wonder if their machines just run and call people all weekend even though they have no live people working to talk to the people their machines are calling.  Anyway...it supposedly is some marketing research thing.....so I guess the "do not call list" does not apply to them???