I know that some interior panneling on my car seem only to squeak at a certain rpm, perhaps it your dash? Anyway, if it's only at one rpm speed, then don't worry. The vibrations from your engine at a certian speed approach the resonance frequency of something loose in your engine compartment (like how a bell or a tuning fork works) and excite it. If it doesn't happen always (I mean at any given rpm), then it's problally not serious. Differential equations, my friends...

ATLD