Strange Noise Near The Throttle Body.

When the temperature is low and the temperature change lot in a day, sometime noise come out from left side of my OHV 12V Vulcan near and under the throttle body. the noise happened sometimes not always. only when the temperature drop down a lot. the noise is high frequency and raspy. Like the noise of loose belt. But there is no belt on this side. It's come out from the engine.