I just bought my second yota, a 86 4 runner, and on the way to work, I suddenly heard a slapping sound under the hood. Checked primary belt and power steering belt. Starts at @ 35 to 40 mph and goes away when slowing down below those speeds, heard it may be the timing chain guides, any thoughts would be great ya'll!

 

A slapping sound is usually the timing chain if there are not belts loose to the touch.