I think my rear BRAKE rotor is rubbing. When I roll my superhawk along with the engine off, it make as "warp warp warp" noise that sounds like a whale in the ocean. The noise goes away with minimal pressure on the rear brake (where the noise is coming from). The noise also comes and goes.

Diagnosis? Thanks!

 

If your brake rotor was rubbing hard enough, it would have locked up and not spun anymore. Have you tried disassembling/removing the rear caliper and wheel, and checking the rotor for any warpage?

FWIW, I have no clue what a whale in the ocean sounds like.

 

Maybe it's more like a seal or a sealion or whatever. "wharp wharp"...
I haven't taken off the caliper yet, but I did visually inspect for warpage, and I couldn't see any. Didn't see any debris either. Either way, it's some kind of low-pitched sqeaky noise that comes and goes. /shrug

 

Rear brake fluid level is ok?

 

Sure is. It's right in the center between the minimum and maximum.

 

It's normal and not a problem.

 

Seriously? That's interesting... What causes it?

 

Disk brakes only retract by being pushed back by the natural variances in the rotor. This is not to be confused with releasing (which can be accomplished by the square seal un-deforming.)

Believe it or not, this is a good thing. If pads were retracted by a spring (like drum brakes, there would be a lot more distance between the pad and rotor when the brakes were applied. It would take longer to get initial bite.

When you stop, you apply your brakes. Then if you roll, you can often hear this shusshing noise. As you ride, though, the brakes are pushed far enough back that they don't contact at all. The pads literally bounce off the minute high spots and completely separate from the rotor.

Disk brakes are actually marvels of both effectiveness and mechanical simplicity. They basically have one moving part (x4 in each SH front caliper.)

 

Huh... Cool!

 

So in the last couple of weeks the problem has gotten worse. It used to only happen under 10mph and now happens until nearly 20mph. It's also louder. I'm sure it's the rear brake as if I push softly the noise gets more high pitched. Is it possible that I just need new brake pads? The bike just passed 10k miles and has never had new pads installed to my knowledge...

 

You can look at the pads and see if they are gone.