I don't know why you wouldn't describe, step by step what you did to install the volume mod? Or at least tell us which specific mod it was? Without those crucial details it's impossible to know what was changed or if you have fully reverted the changes or not.
Lacking key information all I can suggest is that you try clearing the cache from recovery mode (pull battery, replace, then press and hold in order volume up, home, power buttons). If the problem persists then try installing the full, stock firmware with Odin, followed by a factory data reset. That should resolve all issues. Then you can restore your backup. If you don't have a backup, that is a bad habit and in that case you'd have to reinstall your apps again. But at least your system would be stable again.