Tonight while driving the Brick around town, I noticed a whistling sound, kind of like the noise that those toy whistles with water inside them made.

Listening for a moment and trying different stuff, I realized that the car only made the noise between 1,500 and 2,000 rpm, regardless of gear (tried all four drive gears and neutral, same results).

When I got home, after driving for perhaps ten more minutes, the car had stopped making the noise altogether at any rpm. I'm guessing it warmed up and whatever was making the noise closed up or heated enough to stop it.

The temperature locally is about 40 degrees F (it's cold for South Carolina, okay?), so the engine would have heated a little bit after driving (although I didn't notice if it made the noise or not *as soon* as I started driving. I picked up on it after a little while).

We had the valve cover gasket (I think that's the proper term) as well as new motor mounts and something to do with a replacement oil valve put in just a few days ago. Could that have anything to do with the noise?

Any guesses as to what it is? Maybe a(n air) hose problem? My hoses are in bad shape, so that's why I ask.