First, I'm happy to have found this forum for Blazer owners. While far from being a master mechanic, I hope to contribute something to someone, someday!
When the engine's cold and just started up, there is an er-er-er-er-er noise which almost sounds like it's coming from the radio. It speeds up with increased engine rpm, to a point, then stops. Back at idle speed, it returns. When the engine warms up, it disappears. The radio is off. The A/C is off. I recently replaced a tensioner pulley and eliminated another noise. Checked all other accessories on belt drive. Could this be a distributor noise?

 

HMMM! I 've never heard a dist loud enough in the unit when running,and I have had plenty go south in 36 years of owning GM trucks! Maybe pull it and spin it by hand-if any resistance is felt:replace it! Good Luck! step66

 

I checked again, and it's not the distributor. The serp belt was removed and pulleys all seem ok(replaced Tens. pulley). Noise is in the front, actually. Belt is like new. Spraying water on belt quiets noise. I wonder if buying another $30 belt is the right move. Old belt has about 20Kmi on it.

 

-Check the tensioner,any abnormal movement?-Could be the water pump as well-getting ready to go-all easy fixes!
Make sure all accesories(PS,AC,ALT) spin well!
Best to you!