Yes; a common problem since the cocking slot in the piston is a tad too deep. Initially the "mushroom" foot on the cocking lever contacts the end of the slot nearer the top (angle of lever!) and tries to stay in this position due to the loaded friction between the mushroom and the end of the slot. Once the load increases, it breaks free and the mushroom smacks the bottom of the slot creating the "click"!
A solution I have used with quite a few BrumBows is to fabricate a spacer "button" from Delrin which is inseted over the mushroom and ends up in between th cylinder and the cocking shoe effectively reducing the movement and eliminating the smack! I think I re-invented this some while after Venom/V-Mach as I found out later, so don't claim originality!
I attach a sketch of the details I use successfully if it is of any help! I am a BrumBowholic (had twelve at one one time)!
http://freepdfhosting.com/6e2d867369.pdf
atvb
David