when i add a filter all the audio is going crazy. its like someone is scratching their microphone while eating doritos as soon as i add a filter.
I know it wasn’t me because I eat Fritos. 
What version is your Shotcut, which filter?
i have shotcut version 18.07.02 and i tried alot of diferent filters like the zoom and text filters and the sound was the same (super bad).
You need to provide much more details for you to get help and if it is a bug to get it fixed for the next release.
Read this: https://forum.shotcut.org/t/requesting-support/6161
You are probably experiencing the audio preview bug that appeared in v18.07. It was already mentioned in the forum several times, but I know no one bothers to search and read. Did you export it and verify it is a problem there? New version 18.08 with fix for that will be available by tomorrow.