When I grab the front brake there's this high pitch kind of electrical whirring noise. Not sure how to describe it, almost sounds like the noise a cicada makes. Is this normal? Anyone else have / hear it?
I should clarify that it's my mountain that makes the same sound under heavy braking, the s10 does it at a light touch too, but under heavy braking it is significantly louder. Worth checking it again on a ride?
Sorry, don't want to teach to suck eggs just giving you some background...
Brake pads have metallic and other non-metallic particles in them rubbing against a metallic disc. You will hear noise from this. The choice of materials is a trade off to provide life, refinement and safety given extremes of operating environment. 600°C+, high clamping force, 1,000,000's of applications during its life, low weight for sprung mass, corrosion resistance, etc.
You may also have surface corrosion on pads and discs that you may or may not be able to see. (This is not a design fault...there are very few materials suitable for a friction couple for disc brakes).
The rotor has holes in it which will impact on the sound generation. The rotor also needs mounting to the hub...
Friction varies with pressure and temperature and also the friction coefficient of the friction components change continuously.
Surface features on the rotor or pad can also impact all of the above like machining marks, dirt, water etc...
It's no wonder there is sound generated. Metal rubbing on metal!
"Sound" is transmitted directly and also transmitted through suspension, body panels etc. Some bikes will filter out some sounds differently to others.
As soon as you pull in the brake lever you advance the pistons in the brakes taking up clearance generated by piston seal rollback (designed to pull the piston back after each brake application to allow clearance between the pads and disc to stop heat generation and reduce residual drag) moving the pads into contact with the disc.
Some level of noise is normal and is present on every brake ever produced!
Just to be on the safe side though just check around your brakes to make sure everything looks clear and OK and you have friction material left on the pad backplates.
The subject has been covered pretty comprehensively. My only additional thoughts are that it could be a very slight run out on one of the discs (very difficult to identify accurately unless obvious witness on the disc), or maybe the bobbins sticking & not allowing the disc to float freely.
If the brakes work OK otherwise, just check out the suggestions & try giving the bike a few hard ABS inducing stops to ensure the disc surfaces clean of any glazing/contamination.