Sounds like gear whine to me.

 

My control arms had spherical bushing instead of poly and I could hear gear whine that I'd never heard before after they were installed. I doubt that anything is wrong. You are probably hearing noises that have always been there but buffered out by the rubber bushings. Gear whine changes tone as speed increases.

 

Is the drive shaft angle off? Not sure if your arms are adjustable, but I have the spherical bushings on one end. I lengthened them during install to line up the axle holes and when I test drove the car I had a horrible grinding/whining noise. Ended up adjusting the arms back to stock length which realigned the drive shaft and all is well.

 

My LCA's are non-adjustable. The noise is pretty loud and annoying. It's almost like a whirrring sound that changes tone with speed. I hope it's not gear whine....

Would it matter that on the passenger side, the suspension wasn't "loaded" when I installed the control arm? I was having trouble getting that side to line up so i disconnected the shock to let the rear-end droop more and that way I could more easily move the rear end to line up the bolt hole.
I did notice while I was under there that my pinion seal was leaking but I never see any drops or puddles on the ground so it must be only while the car is moving. Could low fluid in the diff be causing the whine?

Edit: I'll try and get a video of the sound tomorrow morning and post it. Maybe it will give some more clues.

 

if it changes with speed/rpm it is most likely gear noise

 

Did you accidentally install a Kenne Bell?

 

When I installed J&M Lower Control Arms, I had the same whining noise that you were describing. I thought something was wrong so I reinstalled the stock ones just to see and the noise went away. Reinstalled the J&M's and it came back. Its just gear noise because the rubber bushings in the stock control arms were created to make a nice comfortable and quiet ride for a street car. As soon as you install poly or solid bushings, more NVH is going to occur. If it didn't make a little more noise, then ford probably would have used poly bushings from the factory considering they aid in handling and traction. The noise you are hearing is totally normal and I wouldn't worry about it one bit.

 

Yeah, I guess I was just concerned bc I can hear it over my loud exhaust(o/r pipe/shorty headers/slp catback with the radio on a moderate level. I'm going to take it for a longer drive and see if the car falls apart on me....lol

 

I didn't notice you listing a gear swap. It lasted this long with that noise, you can just hear it now b/c of the increase NVH of the control arms. I think much of the dif noise is due to how mustang are put together, they do a great job of sending resonance through the body. I had a tire shop try to tell me my axle bearing where going out. When I pull the rear end apart to swap gears a year later, they were perfectly fine.

 

Yeah, I think I was just being paranoid honestly. This is the only suspension mod I have ever done so it was all new to me. The noise is annoying but not unbearable.