The Volume on my Mac Keeps Going Down

I have a 2017 Macbook Pro 15 inch with touchbar with macOS 10.13.4. I don't know why, but every time I connect headphones or anything in the input jack, the volume goes down so much that I can barely hear. When I try to raise the volume I can't because it is already at 100%. This problem continues even if I unplug the headphones. The only way to solve it is by rebooting the machine but, is there a way of fixing it without having to reboot the machine every time I connect the headphones?

Thanks in advance.