1990 Toyota Standard Pickup 2WD

Hi,

Today I noticed I got a weird "squeak" or "whistle" coming from under the hood. Lifted the hood, can't pin point where its coming from, consistent noise every 5 seconds. There is less that 87,000 miles on the truck. Hard to tell if its coming from the intake side of the engine or the fuel injection side, it only makes the noise when it is being driven, not at idle. Do you guys have any ideas?

Thank You