Whats causing this garbled text below my pages? Hoping someone might have experienced this and know the culprit code. This keeps appearing below some pages intermittently. Only on logged in members.
You could try searching for part of the string in your codebase.  If you have SSH access then you could run something like:

cd /path/to/document/root
grep -r "W!b\EU6" .


Otherwise if the file is on you local computer then you could use any search tool to look for "W!b\EU6" (those particular characters are from the last line of your screenshot.

Note that it may not be in the codebase.  It could be in the database or could be the output of some function such as an encoding function.  You could check if it's in the database by dumping the database to a .sql file (not compressed) and searching in that.

If you find it and are not sure what to do with the results then paste them here for further advice.