Higher volume distorts the sound

I have Kenwood (KSC-SW11) in my car and I encountered a issue in it recently. When I turn the volume up , it starts to distort the sound.So, I can't play it in higher volume.I don't increase the volume to it's maximum.But the sound distorts.What can I do to solve this issue? Should I take this to repair center?
 
are all connections and setting as per the original install?
check that things have not come loose or been inadvertently damaged and all switches and filter settings are nominal.
are all the head unit setting correct?
power connections ok?
 
If you're using the speaker level inputs to that sub: turn the sub all the way down & start turning the deck up. If you can get more distortion free volume on the volume knob than you could with the sub turned up, then the subs input sensitivity/volume was simply turned up too much. Turn the sub up till it wants to distort & then back up a little.

If the sub's not audibly loud enough for your taste at that point, unfortunately, that's about all it's going to do cleanly. To get more, you need to have bigger.

There is another possibility, and I mean possibility: If you're using the RCA inputs, there are 2 different voltage levels in the RCA output world now, 2.5v and 4v. If you're running a 4v output from the deck into a 2.5v input, it could overdrive the inputs on the sub. If you're running a 2.5v output from the deck into a 4v input on the sub, the deck output might distort before the sub gets to full volume. Usually a mismatch just means adjusting the subwoofer output level on the deck & things straighten right up.

At any rate, there's a couple more ideas to check out before hauling it in to get fixed.

Todd