Mysterious noise

[jaykoo511]

Hi all. My bike is Santa Cruz Blur with Mavic wheels and Juicy 7 disc brakes. I hear a strange sound coming from the rear of the bike whenever I hit about 22-23 mph. This sound is pretty consistent whenever I reach this speed. The sound can best be described as "metallic singing/rattling sound." I cannot seem to duplicate this sound when the bike is on the stand. I initially thought that the rotor was vibrating and hitting the pads but the rotor does not seem to be loose. I "plucked" all my spokes but cannot seem to get it to make that same sound. Does anyone have any thoughts as to what is causing this sound or how I can trouble shoot it? Thanks.

[DaveM]

If the sound goes away when you apply light pressure to the brakes you can assume that is the source. Do you have wheel reflectors? Those can make weird humming noises at speed sometimes. It could also be some small part like a brake hanger, etc. vibrating. Hard to catch those without putting tape or a rubber band on various things to block vibration until you narrow it down.

[JonB]

It's quite possibly the pads vibrating and bouncing off the pistons. Whack a bit of copper grease on the back of each pad, should stop it for a while (just don't get it on your rotor or the front of your pads)

[jaykoo511]

What is copper grease? Could I use some white lithium grease that I already have? Thanks.