I just got into bass a few weeks ago, and i notice sometimes when im playing the the low E string makes a slapping kind of noise some times. especially when i have the string tuned lower, like C#. Is this just normal, or am i doing something wrong?

you can here what im talking about:
Listen to CKY.
It is normal.
When the string isn't tense enough, it gest a bit floppy and makes fret buzz noise.
Get a new pack of sttrings with higher guage to avoid it (if you play in C# all the time).
Sometimes, the neck being a bit curved can make this happen, but it's not really common.
You could also be hitting too hard (Steve Harris does that intentionally as part of his tone), if it bothers you too much you could use a higher action (string height) or strings of a higher gauge.
Professional lurker since 2009.
Fret slap is annoying as hell, but it is a fact of life with the electric bass. The only total cures are to raise the action to ridiculous heights, or to use a fretless bass. The good news is that it rarely comes through the amp, so once you learn to put it out of your mind, all will be well.
"Maybe this world is another planet's hell?" - Aldous Huxley