Fix a whistle on a 2007 G6 3.9L Convertable from the exhaust

here is a link that may help you find the problem and fix it :-
http://www.2carpros.com/articles/car-whistling-noise

check hoses for leaks or if they are disconnected

it may be a turbocharger if so equipted, lots of turbocharged cars whistle as the unit gets older..only other thing I can think of is something with the exhaust system.. get it looked at by putting the car up on a lift and inspecting it..now some cars also whistle thru the radio ..this is called alternator whine and is usually correected by a filter in the power line of the radio...good luck

Possibly,
Do a compression test on the engine to confirm or rule out a breached head gasket. If the gasket breached you could get antifreeze leaking both internally and externally causing both white smoke and the squealing belt and have a oil leak. The gasket is one of the few things that separate these systems.

You have ruined the exhaust converters with the diesel fuel

Its that dealer next to usless?

Your cooling system is not working properly. You should have this looked at immediately. Could be a stuck thermostat. Is your engine temp running hot?

Micro switch malfunction in bow of roof next to release handle.

Is your car a turbo???

If yes, that is the turbo winding down. The turbo is powered by the exhaust gasses from the engine.

Turbos are noisy if they are working. If you have the 2009 6.4L they (twin turbo) should be pretty quiet unless you have aftermarket items installed. If no aftermarket mods have been done have the coupling joint between the turbos and the outlet gasket checked by your dealer.
If it a 2007 as the heading says the original air filter and exhaust muffle a lot of the turbo whine but not all.

the filter in cat. conv. is broken will need to be replaced,is or may cause exhaust restriction flow!