Hi!
On my new commuter bike build (based on 2007 Trek 6000 with 3x9-speed deore), I cannot set up the front derailleur in such a way that when I'm in the middle chainring, there won't be any FD rubbing when in the extreme positions in the back. I get, that big+big and possibly small+small will create some rubbing on the FD. But I've never seen rubbing when using middle+[small or large]. 10+ speed systems have trims to get around that. My 8-speed tourer doesn't have that issue. I believe my FD is mounted properly.
Is 9 speed just in the middle of everything and has this issue, or is this not supposed to be the case?
Just for context: chain and cassette are new 9-speed components (KMC, SRAM), and crankset, chainrings and RD are original Shimano parts in good condition.

Thanks!

https://www.sheldonbrown.com/deraile...ent.html#front Sheldon Brown says that adjusting FD is not an exact science. You can check/adjust the mounting of your FD following his guide.
There are some similar threads about the FD adjustment.
I am not an expert myself, just a home mechanic. I have experienced some front derailleur rub on both 8 and 9 speed
Also, you did not say if the FD was the original one.

I strongly believe it is original (got the bike used). The cage length looks right to me. Will check all that on the weekend.

Quick, late update: it is the original derailleur. It is set up at about the recommended height from the chainwheel.

You didn't mention what shifters you have, friction or indexed for the front. If you have rub when in the middle chain ring and both the smallest cog and largest cog, then may I suggest you adjust so that you don't have rub at one extreme, then just trim at the other extreme. Not familiar with your bike but does it have short chainstays; that can affect rub. Just keep playing with it until you are happy and it shifts well.

I have been playing with it a bit in the last little while and I've arrived at a configuration that is good enough.
I have indexed MTB shifters at the front without ability to trim with shifters. I think, the chainstays are a bit on the shorter side.

Move the left lever after every rear shift to re center the chain for clearance..

I find this simple to do with my friction shifted front derailleurs..

I am on index shifters.

too bad, I stay away from them, personally, but cope with others, when on the repair stand , right in front of me..
Your LBS, seeing it there, might help.