Grinding sound at RD when out of saddle

[cyan]

Second largest cog (25T) at the back and big chainring at the front. When out of saddle and pushing some power, grinding-like sound/feel at the back (likely the RD pulley rather than the cog, though not 100% sure). When seated and with less power, no grinding. Can only imagine what would be like for the largest cog...

What gives?

[oldpotatoe]

Second largest cog (25T) at the back and big chainring at the front. When out of saddle and pushing some power, grinding-like sound/feel at the back (likely the RD pulley rather than the cog, though not 100% sure). When seated and with less power, no grinding. Can only imagine what would be like for the largest cog...

What gives?

Try swapping the rear wheel..what wheel/hub is making noise? Since you are cross chained, could be how much tension there is on the rear der also, as in maybe chain too short. Or just severe angle of the chain to rear der/cogset..noise coming off chainrings...

[Dave]

Using the big ring and next to largest, pedaling out of the saddle with a high torque, isn't the best thing to be doing. The cross chain angle alone may produce some noise, that is normal. It's telling you to quit doing that.

[fa63]

I frequently cross-chain in the 50/28 combo (on a 11-32 cassette) under power; makes no more noise than in any other gear. SRAM Red drivetrain.

[muz]

Could be chain rubbing the FD cage. I know you said the sound is coming from the back, but IME it's very hard to localize these sounds.

[tomato coupe]

I frequently cross-chain in the 50/28 combo (on a 11-32 cassette) under power; makes no more noise than in any other gear. SRAM Red drivetrain.
Yeah, every bike I own can be ridden in the big-big combo without any noise, even out of the saddle. (50/34 with 11-23, 11-25, 12-29, 12-32)

[cyan]

Checked again, not a FD issue, the grinding comes from the back. Yes, it is cross-chaining, but not a big-big so I'd expect it should work without grinding, plus it was working before when the bike was freshly built.

Chain or pulley wear?

Or could it be a limit screw or RD indexing issue? I've touched both since the bike was built.

[muz]

Every thing on the bike flexes to some degree, more so when you are climbing out of the saddle. You need to have a lot more clearance than what would appear to be necessary on the workstand. With the bike on the ground, apply the front brake and put a lot of weight on the pedal (at 3 o'clock position), observing how the BB moves sideways, see if you can spot any issues.