Whistles during start and acceleration

For the last several days I have noticed that my car has been whistling when I start my vehicle and when I accelerate. Sometimes it continues for as long fifteen minutes, but then ceases. What could be the problem? I have been told the air filter, transmission, and I was even told that it could be my alternator charging. My check engine light is not on and I have had it checked on the diagnostic machine, but nothing comes up on the computer. Please help me with this issue, considering I do my best with keeping up with the maintenance, ie., oil changes, brakes, plugs and wires etc.
Thanks in advance for any help you can render.