You can replace the sound I believe, but this doesn't work when sv_pure is enabled. Or turn up your hitsound.

Max out the hitsound volume and decrease your regular volume. I need to use 1 and 0.15 respectively, so the numbers are not accurate.

//volume control
alias "vol0" "volume 0; unbind f2; bind f3 vol5; echo [VOL 0.00]"
alias "vol5" "volume 0.05; bind f2 vol0; bind f3 vol10; echo [VOL 0.05]"
alias "vol10" "volume 0.10; bind f2 vol5; bind f3 vol15; echo [VOL 0.10]"
alias "vol15" "volume 0.15; bind f2 vol10; bind f3 vol20; echo [VOL 0.15]"
alias "vol20" "volume 0.20; bind f2 vol15; bind f3 vol25; echo [VOL 0.20]"
alias "vol25" "volume 0.25; bind f2 vol20; bind f3 vol30; echo [VOL 0.25]"
alias "vol30" "volume 0.30; bind f2 vol25; bind f3 vol35; echo [VOL 0.30]"
alias "vol35" "volume 0.35; bind f2 vol30; bind f3 vol40; echo [VOL 0.35]"
alias "vol40" "volume 0.40; bind f2 vol35; bind f3 vol45; echo [VOL 0.40]"
alias "vol45" "volume 0.45; bind f2 vol40; bind f3 vol50; echo [VOL 0.45]"
alias "vol50" "volume 0.50; bind f2 vol45; bind f3 vol55; echo [VOL 0.50]"
alias "vol55" "volume 0.55; bind f2 vol50; bind f3 vol60; echo [VOL 0.55]"
alias "vol60" "volume 0.60; bind f2 vol55; bind f3 vol65; echo [VOL 0.60]"
alias "vol65" "volume 0.65; bind f2 vol60; bind f3 vol70; echo [VOL 0.65]"
alias "vol70" "volume 0.70; bind f2 vol65; bind f3 vol75; echo [VOL 0.70]"
alias "vol75" "volume 0.75; bind f2 vol70; bind f3 vol80; echo [VOL 0.75]"
alias "vol80" "volume 0.80; bind f2 vol75; bind f3 vol85; echo [VOL 0.80]"
alias "vol85" "volume 0.85; bind f2 vol80; bind f3 vol90; echo [VOL 0.85]"
alias "vol90" "volume 0.90; bind f2 vol85; bind f3 vol95; echo [VOL 0.90]"
alias "vol95" "volume 0.95; bind f2 vol90; bind f3 vol100; echo [VOL 0.95]"
alias "vol100" "volume 1; bind f2 vol95; unbind f3; echo [VOL 1.00]"
vol15

/hitsounds
tf_dingalingaling "1"
tf_dingaling_volume "1"
tf_dingaling_pitchmindmg "255"
tf_dingaling_pitchmaxdmg "1"
tf_hud_num_building_alert_beeps "1"