You'll struggle to fit any fans into that gap. What's the thickness? They are an openframe design which means you're unlikely to find something the same.
Instead, have you got space on the outside of the heatsink? Then just zip tie on a 120mm fan and that should do the trick.
As for the high pitch noise, if it's a sort of squealing sound under load then that's probably the card, not the fans. A lot of high powered cards do this.
thaks for your reaction. which gap do you mean please? I thought i’ll separate the cooler from the card for the fan replacement and re-fit it with a new layer of thermal paste...
adding a new fan to the outside is something I’m considering too but I’m affraid it wo’t be as effective as the original possition of the fans (inside).
I’ll check if the pitch noise is there after the fans are disconnected thanks.