Hello. With my HD205 headphones, in the left headphone it has a small crackling noise with certain songs.. I don't know if its meant to be like that? Its done it since I had them first - Happens to bass sounds.. they are kind of.. overtaken by a small crackling noise.. =/

There are two likely causes for this. One is much, much easier to fix than the other.
1) You are turning up the volume too much. Headphones, especially non-top of the line headphones, are not meant to be listened to at very loud levels. In this case, the crackling you are hearing is the speaker trying to reproduce a bass sound that is "clipping", or exceeding the maximum output level for that system. Remember - headphone speakers are very small; they have a harder time producing low sounds accurately. The solution is to just turn them down a little.
2) Assuming problem 1 is not the problem, the other likely issue is that they came with some sort of mechanical defect built in. If you are not playing them loudly, but you are still getting a crackle, especially if it is only on one speaker, they probably are broken. It is probably the jack itself, or the wiring leading up to the earpieces. Either way, it is not a terribly hard fix if you have some electrical know-how, but if you don't, there are plenty of people who can rewire them for much cheaper than it would be to buy a new set. However, if this has been happening since you got them, I would call the manufacturer first and see if they will replace them. Sennheiser tends to pride themselves in the quality of their equipment, so I would not be surprised if they sent you a replacement set.
Hope this helps!