.htaccess and 500 error, extra character added

I am having a weird problem. Every few days I go to my website and get an “Internal Server Error” – Or 500 error. I go into the .htaccess file of the site and notice it’s been altered. One character is added at the end of the file.

It’s easy to fix and continue on, but it keeps happening. htaccess permissions are 644 and the error logs don’t say anything about this so I don’t know where to start.

Anybody have an idea as to what’s going on or point me to some information on this issue?

here is the “altered” htaccess code:

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index-php [L]
</IfModule>

# END WordPress
s <---See This?!

Assuming you’re on Linux, if you go to your wp-content/plugins folder and run

grep -R 'htaccess' *

it should let you know if any plugins are addressing that file by name