300E Whistling Noise
 

Wondering what the whistling noise I'm hearing from my car might be. It isn't there when I start it up cold but after a while kind of sounds like a car with turbo but is very light. Changes with speed of engine and I know my little plastic cover is in place on my torque converter cover. It isn't as loud as what it sounds like with that cover off and doesn't sound like a pulley or Alternator whine. More like air escaping. Can hear inside and outside of car (towards front). Anyone had this before? Car is 1991 300E.