I have an aluminum 2016 Giant Defy Disc with Mavic Ksyriums. Under load I'm getting an intermittent scraping sound. The occurrences seem to be inversely proportional to rear skewer tension. Tightening seems to help. So yes, the obvious easy answer is tighten the quick release another half turn but it's already pretty tight, and I'm thinking the root of the problem is in the dropout spacers, maybe. ??? I'm thinking the scraping sound is the disc when the wheel is pulled slightly out of alignment. What say you pro's, am I thinking about this logically?

Maybe the bearings are too loose and tightening the skewer just compresses the axle more to take up the slack.

I hadn't thought of that. I'll pull the wheel and check for any play. Thanks

A simple test would be to spread the rear pads away from the rotor and then ride the bike (without using the rear brake to reset the pads). If the sound still happens with 3 or 4mms of gap between the pads and rotor then the noise is likely from something else. Andy

Had exactly the same issue on the front of my 2016 Giant toughroad, was prominent when I peddled harder, drove me crazy! I did the skewer thing too, which helped a bit, but I knew that was BS because all that gear is meant to have a specific tension. It turned out to be the body of the disk caliper brushing the rotor of all things. You can easily get down there with a torch and check the clearance.

Like I said, not the pads, but the aluminum body itself. If that's the case with you you'll find scratch marks on the disk rotor, inboard of the pad contact area. I loosened the two mounting bolts and repositioned the caliper and it went away. Be Advised though that they can be notoriously tricky to align, there is a procedure, google it. I was lucky, I've done it before and jinxed it on the first go.

So no obvious play in the axle. The disks look pretty normal but I did notice some missing paint on the rear caliper in a few places. Hard to tell if it's scratched up from taking the wheel on and off or from interference while riding. I'm going to re-align the caliper to see if it changes anything. I'm betting that's it.

Coominya was on the money. I realigned the rear caliper and that seemed to take care of it. I did 30 miles last weekend and didn't hear the scrape all all. Thanks