[filian]

If it ends up not being the heat shield then it could possibly be the serpentine belt tensioner. I had a radddle type noise come from it when i accelerated. It would make the noise between 2500-3000 rpm. My tensioner was located under the alternator. just needed to be tightened up

 

[filian]

i wouldnt think its anything with the exhaust bc the whistling only on acceleration means air leak being sucked in.