Weird problem I’ve had for some time… The car makes a noise that sounds like a slipping belt and only does so at a speed of 15 mph or more. Its a manual and I know it can’t be a belt because I’ve done a little testing while driving. I’m going down a hill, put it in neutral, turn the engine off completely and coast down the hill and the noise is still there. So nothing in the engine is turning at this point, I’m just rolling. So what is moving at this point that could make such a noise?
It also makes the noise when the engine is running and what’s weird is I can almost make it go away (the cycles of the noise become less and less frequent if that makes sense) while in gear if I apply the gas just a touch to a point where I am neither accelerating or decelerating. Any ideas what this noise might be?
Could be a bearing, but more likely a brake wear indicator. 
Compliments on your having eliminated engine sources, however.
I thought of the brakes so I removed those too before taking on the hill 
haha kidding! I’ve changed brake pads many times before and it’s not that noise. Bearings could be a possibility. More testing needed… any other ideas out there?
You can always elevate the front end, spin the wheels, and see if there’s any roughness to the spinning.
My vote is for a wheel bearing.
depending on what car you have it could be any u-joint in a rwd or fwd yeah most likely the wheel bearing. Did you do the wheel bearing tests? Turning left and right to see when it goes away or gets louder. Find a open road where you can turn a corner at 15mph or when you hear it.
A tensioner is another possibility
Don’t dismiss the brake wear indicators until you have had an up close look. A binding caliper can wear the pad down quickly on one end of one pad.
Is your cooling fan electric or belt driven?
Unlikely to be the radiator fan b/c the sound occurs with the engine turned off.
hmmm … good clue about the sound remaining while coasting w/the engine off … hmm … well, I’ve had a squeaky sound on my truck caused by a u-joint in the drive shaft that was running a little dry and needed a lube. That’s a possibility if your Suzuki is similarly configured. & I’ve had squeaky noises caused by the brakes too, but only noticed those when turning, not ever just going straight & not touching the brake pedal. If you don’t hear that noise when barely applying the brakes, discount that idea. The only other thing I can come up with, sometimes those boots on the CV joint will bunch up and you get rubber rubbing on rubber, which can produce a squeak. Might be worthwhile to have your shop take a look anyway. Wheel bearings can make a noise, but not usually squeaks. But that’s still possible I suppose.
Worn wheel bearings usually make a groaning noise when curving left or right at moderate driving speeds but if they’re really bad they can make a shrieking noise. If they get to that point they may seize up causing the wheel to lock up causing disastrous consequenses. I’d get it looked at ASAP.
The tip-off to me is that the sound stops when niether accelerating nor decelerating.
When I hear that comment, I think of a problematic differential too.
Last school year while waiting at my Grandson’s bus stop an older Honda Civic passed by at about the same time every day for 2 months. I could hear a wheel bearing “singing” for 2 blocks coming and going. One day it disappeared and never returned. Hmmm…
The “singing” or the Honda?