I have a 2004 Pontiac Vibe that has recently been making a clanking sound only when the heater is on...more specifically it won't do it when it is on the first fan setting but it does it on all of the other faster settings. Also, the heat won't get hot unless you are driving down the road aka you can't start it up and let it warm up and defrost the windows :'( I know there are more but I can't think of them right now...
p.s. sorry for my inept search abilities...as I know this has probably been covered for the last 10 years...