Try using the highest octane gas available, try a bottle of the redline injector cleaner, go for a long drive on the highway, change the oil.
Also double check the oil level is not too low or overfilled.
It could also be increasing the revs as the ac pumps engage, this may be especially happening on hot days or when not moving fast (less cold air), especially if the coolant is super old or of unknown age.
Could it be an obstructed fuel pump? If rust/debris/whatever else interrupts the fuel supply? More senior member would probably have a better idea. Like others have said hard to tell.
Sometimes my car "whistles" a bit, have not considered this an issue but it could be a normal sound?