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Feedback knock at low load.

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Hello all, have been having a very annoying problem with my subie. I have a 2005 legacy gt with a turbo back exhaust and a pro tune. At around 2400-3000rpm anything above 2-4psi of boost will cause knock on my access port and what feels like the engine choking or losing power.this does not happen at wot, or if I let the RPMs build up without boost. I’m at 110k miles, no check engine light. Original 02 sensors, cleaned maf a few months ago. Tuner thinks it’s a fuel pump as he’s had to add more fuel when he shouldn’t have to. Any insight would help a lot. This knock happens on his tune, on the base Cobb tune and oem edu.
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Are you AFR looking good...are you running lean ?

If its the original fuel pump and filter based on the mileage you might be due to change them....if you can't yourself, have the fuel pressure checked. If everything looks good, move on to the other stuff...a smoke/leak test would also be recommended.

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