Motor RCout oscillation

I have an issue with a 500 size quad that I’m not sure how to attack. Tuning is good, vibes are OK (small amount of clip at fast speed). At hover all is well but with horizontal speed the motors are being commanded to oscillate.with a fairly high range of magnitude. This craft actually flies well but this is bothering me. Craft description:
1.7kg AUW
3508-380kv Motors
Some older BlHeli_S ESC’s
13" CF props
6S Power

Take a look at the FFT and the peak at 29Hz (post filter). I’m using the Notch filter to handle a 59Hz mode and it’s harmonics perhaps I should address this 29Hz mode?

So this could be your EXPO setting. If your EXPO is wrong then at higher throttle your PIDs will be wrong. On my miniquad I had to reduce EXPO quite a lot to avoid high throttle wobble. This also could easily not be your problem - @Leonardthall s estimates for EXPO based on prop size are surprisingly accurate.

Thanks Andy. I did set it roughly from the graph in the Tuning Process but now that you have highlighted that I’ll try some mods of the value and see what happens. There is nothing of high value on this craft so I don’t mind experimenting.

Edit: You were right that this is the driving factor for the issue. I dropped EXPO from .687 to .6 and this is directionally correct to address it. In fact it’s not bad with that one change but I’ll try a range and see what happens. Thanks for the assistance!

Note: Before trying this I enabled a fixed notch filter at 29Hz and it effected basic control stability and caused a low frequency roll/pitch oscillation. It’s too low to address with a filter I suppose.