I have a 2005 Mercury Mountaineer Premiere. Once I set the speed on cruise control (which is usually 69 mph on the highway) I hear a high pitched whine. If I bump up the speed to 72 or so it goes away for a short time and then resumes this very irritating sound. Drives me nuts. Any ideas where I should start to remedy the problem?
It only does this with the cruise control on? Or does it also do it if you leave the cruise control off and control speed manually?
It only does it when the cruise control is “on.”
Well, I’ve been thinking but the only possibility that really comes to my mind is some kind of electrical noise/interference from the control circuit. But I’m also assuming that this is a cable controlled cruise control as all of the ones I’ve ever had are cable controlled. I supposed one other possibility might be if there is some kind of vacuum controlled system in which case you might get some kind of whistle out of a vacuum leak.
Can you compare the whine to anything else - e.g. does it sound electrical? or like a whistle? Can you give some idea of where you think it is coming from?
So I think the short story is that I’m clueless (apparently) - though at the very least I’ve given your Q a couple of bumps and there are other people up here smarter & more knowledgeable than I.
Thank you for your concern and thoughts. I would describe the whine like one that you would hear when taking a hearing test. Very high pitched and never wavering. One solid high pitched whine. I could also describe it as what it sounds like when your ears are ringing. No – my ears are not ringing 
When I turn the cruise control off, it stops right way. I am always dealt strange problems it seems. I have yet to run this by by my local mechanic, but I plan to do so very soon. So far I have just turned the radio up to block the sound out. Too lazy to turn the cruise off and use my foot.
I do believe cruise control has a vacuum input, possibly vacuum leak somewhere there.
When it finally warms up outside (due maybe this week)in the Midwest, I will do a little searching around under the hood and check to see if any vacuum lines are loose or whatever. I surely hope that is all it is. Not sure how much a new cruise control would set me back.
You folks’ assistance has been more than appreciated and I thank you all very much!
That annoying whine is the siren on the police car behind you.
Can’t help with how to remedy that …
seldom is cruise control require replacement. It is usually the brake switch solenoid for it failing, or some utilizing a vaccuum and a hose leaks etc. Do not let any one sell you a complete cruise control