So, I’m a rather well-endowed lady, with few options (not to mention $$$$) for new bras. A couple of the ones I have (my favorite ones too!) have developed what can best be described as a squeak. I’m pretty sure that its coming from the little plastic adjusting thingy on the strap. I only notice it on one side. Its really annoying and getting noticable when I move even a little.
Has anyone ever noticed this or know of any way to fix it? 
Two suggestions:
Don’t dry your bras in the drier.
Rub a bar of soap lightly over the strap and little plastic thingie.
Maybe your squeeky clean.
I hate to intrude, but see this post and the whole thread.
Take it off.
There’s no way we can help without seeing some pics first. 
Oh, thanks a lot guys. 
You could always just…take it off. No squeaking then, right?
I’d say…use silicone.
I’d wrap the offending fastener in several layers of duct tape. That should change its rigidity enough to prevent squeaking.
A somewhat less ‘Red Green’ approach might be to unhook the fastener, and paint the two rubbing surfaces with a bit of fingernail polish. That should alter the frictional coefficient and or the resonance of the fastener.
I can certainly stop by with some oil.