A little saliva build-up in the mouthpiece is normal, and when reed get’s a lot of it you can hear it so it needs to be wiped off. Your problem sounds a bit more severe. I wouldn’t know why,we;’re all different and so only you can try to control it. Try to be more aware of what’s happening while you’re blowing, and try to keep less saliva from building up, maybe by being aware you can decrease this problem.