1995 Silverado makes high pitch tea kettle whistle when cold
 

My 1995 Silverado makes a high pitch tea kettle whistle when the temperature is about 30 degrees. I have had a new PCV valve put on it, a new alternator & drive belt installed, water pump, fan clutch and idler pulley installed and it still whistles like a tea kettle. When the truck is warm it will still whistle periodically. I have spent a ton trying to get rid of this noise and to say I am discouraged would be an understatement. All work has been done by professional mechanics and the cost and parts have not eliminated the problem! If anyone can tell me what on earth is causing this problem I would greatly appreciate it. My last thought is the manifold gaskets or throttle???
Thanks!

Welcome to the forum...

I would concur, you have a vacuum leak...might try spraying around the engine with starter fluid to see if you can find the leak, any ingestion of the fluid into a leak should change the idle...

Thank you! Where should I spray to test for leaks? Or do you think I should have this done by a mechanic?

After spraying starting fluid on all gaskets the only idle stumble I could find was inside the opening of the passenger side exhaust manifold heat shield assembly towards the front of the engine. It was in the opening in the aluminum shield in front of the heat riser hose. The engine almost stalled out when the fluid went down inside that opening.

That sounds like its drawing it in at the warm air intake for cold starting. I would suggest hitting the base of the throttle body and along the intake manifold. It may also be worth investing in a harbor fright mechanics stethoscope...