mystery squeel at start up

[mcs336]

I have an 86 Chev PU with 305 V8 that I bought about a 2 months ago.
Has about 107K original miles with no apparent history of any major engine work.
At start up there is a high pitch squeel that lasts about 20 seconds to 1 minute and then goes away. It only seems to occur at cold starts. At times the squeel is very load and can really hurt your ears.
I have done all of the following and cannot figure out what the source is:
1. replaced water pump & hoses
2. replaced alternator
3. replaced belts
4. disconnected the air pump
5. disconnected power steering
Anyone have any ideas on what the problem could be?
Thanks