I've had similar problems with my truck. You will find there is a resistor pack that divides voltage to the fan controlling fan speed. High speed bypasses the pack which is why it still works. The startup noise could very well indicate failing fan bearings--that could have caused the burnout of the resistor pack. The pack usually cost about $20 and is fairly easy to replace--look for it near the fan assembly. If you still have startup noise consider replacing the fan motor also or you will burn out the new pack eventually. Either buy a repair manual for your van or check one out from the Library and make a copy of the wiring diagram. Good luck.