weird noise from gearbox when revving engine

Hello everyone. This is my first post here because I dont know where to look anymore. In 2023.
I bought Citoren C3 2019. 1.2 puretech 61kW. Everything seems fine and car runs alright, I have done major service on the car, replacing all the belts,filters .. ect. at authorized service dealer. Then by pure luck(unluck) one day I was revving my car and found out that some wierd noise was comming from it when in idle at around 2100 rpm. The sound is similar to something like you would find in washingmachine when zipper hits glass in front of it when washing(if you know what i mean). Also the sound is not consistant like it would appear every second or so, rather it appears every few seconds and is not very loud(you really need to be inside of the car,music and ventilators shut down to be able to hear it good.) When i press clutch peddal that sepparates engine from gears, sound is gone at that rpms.(at least I cant hear it anymore). So i went to same authorised service dealer and they said they need to disassemble gearbox too see what is happening because they found out that the sound is comming from there. Ofcourse they said they didn't find anything odd there but a small air gap between 5th gear. They replaced 5th gear and oiled and cleaned everything so the acceleration peddal and clutch peddal are all smooth. They charged me 500 euros. I tried the car down at service center and the sound was really gone. After 7 days I wanted to test that again at home and the sound came back again. I was really angry at them and called them that i will return with my car again because they didnt fix anything... Yesterday my friend came at my house and I showed him the problem while the car was in garage and the sound wasn't there again. Now I was thinking to myself am I crazy or what? So I revved my car a little bit harder at around 4 to 5k rpm and while that i pressed gas peddal a little bit harder to notice that after some path there is some click position of the peddal and you can exceed that position(click happens) and then you can press the peddal really all the way to the flor. The sound then came back again when slowing it again around 2000 rpm. Now I really wonder is that maybe normal that some components in gearbox are doing different sounds when i rev the car a little bit agressively or what? I didnt have a chance to sit in another new C3 with that motor to see if the peddal really goes all the way with or without that click position and if the sound reapears after agressive reving. In general car drives normally with a little judder in 1st and second gear but somewhere I had read that this is common problem on this car model. I really dont know what it could be, maybe clutch or transmission in idle, peddal clicking point(what does that even means in the car or is it broken), something with motor...

Any advice, tip , response, answer would help a lot. For any other question please ask.

I don't know what gearbox is in your car but the manual 5 speed gearbox that used to be in the C3's would suffer a collapsed bearing on one of the gear train shafts.
It's only been 4 years but you could try changing the gearbox oil.
If those guys ACTUALLY pulled the gearbox apart they would have changed the oil. HOWEVER, did they pull the gearbox apart?
If you drain the oil AND they pulled the gearbox out the oil will be clean.

Hello, thank you for your reply.

As I said they are representative service for Citroen vehicles. They gave me the bill for changing part 5 gear and oil changing with service hours of work. They said everything looked brand new in there and they only could assume that there was a small gap on 5th gear so they changed it with all other parts of 5th gear that are in relation. Today I was there once again and we tried to compare sound of gearbox of my car with another C3 with same engine. Now, that car was there some time so we couldnt hear nothing comming from gearbox(Cold start) but from my car you could easly hear when reving the engine that clicking/mixing sound when putting it on 2000revs. They said it would be just additional cost and a lot of work to find out what really is but they said they looked at everything and all looks almost brand new. No errors when testing car PC,no transmittion problems, no clutch problems,nothing to worry about... But still I gave them 500 euros and they didnt do anything but open up gearbox,changed good part and assebmble everything together again. They said it doesn't affect driving and nothing so I can safely drive the car again.

My only concern is that maybe it would do more damage to the car in the future, so i am asking anybody with similar problem,or some expeeiemce with this new model to tell me a little bit more what it could be the problem. I will go to some local mechanic workshops to ask them if maybe they know what is the problem.

Maybe it is the bearing problem but they said nothing wierd about them in gearbox to be found. I can only trust them cause that is not easly to look by myself or local mechanic. Please, any help would be greatly appreciated.