[rdusel]

I have the exact same issue with my '07 GT convertible. High pitched whistle at certain levels of acceleration.
The car is almost 4 years old (it was originally bought in Dec 2006) and 20K miles on the original serpentine belt. I guess I will try changing it this weekend and see if that resolves the problem. Dealer is a bit far away and would charge for the belt anyway.
If not the belt then I will look for the "weep hole".
I'll post back my results next week... I hope this is the answer.
RD

 

[rdusel]

I just tried a new serpentine belt and new idler pulleys, no change at all so I guess I am going looking for a weep hole before I take it to the dealer.
I was surprised that the belt was not in stock anywhere, then I saw how long it is. I don't think I have ever seen one so long before..
Due to the dealer cancelling my after market warrantee ("oops it was a clerical error") I now have to wait 30 days for the coverage to take effect.
arrghh...

 

[rdusel]

Not too bad to change, invest a couple of minutes and remove the airbox, you will be glad you did.
And you will probably need a strong bar to move the motor mount back a hair to replace the spacer. You will see what I mean when you get there..
Rob

 

[rdusel]

This is just depressing. A design defect that turns up at 27K miles (or in my case 20K miles) and isn't even covered by the warrantee.
I wonder if the whistle is internal or from a weep hole in the resonator as mentioned before? Maybe a stainless steel screw in the weep hole will quiet or eliminate the noise.