Wierd AutoSelect problem!

Ok so once i played on a ZombieSurvival server and something wierd happend everytime i scroll it automatically selects the weapon its really REALLY annoying. I once got i new computer and when i then installed gmod there it was there again that really creeps my out HALP. If you have a fix then please tell me its really annoying when me and my friends are making machinima i need to go through all the weapons to find the right one

It’s in the options. Probably under “Advanced”. It’s called Fast weapon switching or similar.