Whine at 69mph
 

New owner and forum member here. Thanks to all for your contributions.

Have a weird problem that I didn't encounter on the test drive. Just bought a super clean 06 F150XLT super cab with 5.4L engine with 58k miles. At about 69mph (1950rpm) I have a whine that comes in. If I speed up or slow down, it goes away. It does not change in pitch, just volume. I think it's more harmonic than mechanical, but really can't tell.

Any ideas?

Alternator. Do a search and others on here talk about it. I have a whine also and thinking about changing the Alternator but haven't done so yet.

Alternator just at a certain speed? I would think it would be the plastic cowling near the windshield. Check to make sure its secure. Put some tape on it to hold it in place and take a drive and see if it helps.

Might be rearend
 

I have an 04 with a rear-end whine that is similar. At 50 mph under acceleration but not deceleration. The alternator issue I have found here is related to cold weather and tight bearings. And not specific to speed. I was told by a mechanic my rear-end was bad. That was 20,000 miles and two years ago. I am not worrying about it.