Heater Core/Blend Door/Heat Problems - Noise from Dash

Hey Guys,
Have a 2005 Passat and having some heater issues. Just had the temp guage senson fixed and now the heater is acting odd. The temp guage shows a constant 190, however, when I turn on the heater it blows warm air for a few seconds then just blows air out with no heat. Then to top if off, there is an occasional buzzing coming from the dash. Sounds like its coming from the duct work, sounds similiar to radio static but not exactly. Any help would be appreciated. I have read where it could be the heater core, or the Blend door malfunctioning...

First thing I'd try is bleeding the system. might have vapor lock in the heater core. Thus the short period of warm air. Don't know about the buzzing. Mine buzzes on lower speeds. For me, it's just the fan coming in contact with the housing.

1) My mechanic used CLR. There's a thread on this. Heater died like your's did. I was ready to replace the heater core, but the CLR forwards and backwards over and over did the trick, So far so good. Hot as hot gets when it's needed.
2) That buzzing noise, does the pitch change/vary with the fan speed? If it does, something's probably touching the blades of your fan.