I bought new speakers, why do they crackle?

I bought Sony xplod 5 1/4 speakers for the front speakers since they were blown I'm pretty positive I hooked them up correctly. But when I turn up the volume to about 21 they start to crackle. I have two bad speakers in the real deck which I expect to crackle but would they effect the front? Because I'm going to change the back too. Will that fix the problem? Also I have a single den head unit (Kenwood) at least 9 years old would that effect things? What would effect the new speakers? Furthermore I have a 94 Honda accord

Infinity or Alpine make the best auto replacement speakers, Sony are flea market quality car speakers at best.

I had some xplods and they distorted too. Switched to Pioneer and no problems.

Too much power most likely.

There are a few factors, but mainly I think you're hearing a lack of power.
Your HU probably produces around 17w rms per channel (you can ignore any peak or max power ratings - that is a meaningless number). Your speakers are probably 35-40w rms each. So you have less than 1/2 as much power as those speakers need to perform optimally.
The other problem is bass. A 5.25" speaker simply doesn't have the physical capability to produce bass with much clarity, or any loudness at all. And when they try to the result is a lot of distortion and poor sound quality, especially at high volume.
Have you tried fading your sound just to the Sony's to isolate the problem. Try that, and also try reducing the bass setting. You might not get much bass out of them, but at least the overall sound quality may improve.

Those speakers just aren't up to the job. There's a handling power expressed in watts, but more important is the frequency where that power is measured. When they say something like 50 watts at 60Hz, which is not all that great, if you hit them with that power at 40 Hz they might only have the ability to handle 30 watts without the voice coils crashing into the magnets. I don't know the response curve of your speakers exactly, but we both know the performance you're getting with them. Turn down the bass, replace them with better speakers, or explore sealed enclosures for them. For now, see what their limit is and hold the line until you get something better. There isn't something you can do to change those explodes into something else.