New Amp/Sub makes pop when HU turned off/on

Today, against my better judgement, I had futureshop install my new amp & sub. I had plans to get a cd deck to replace my factory head-unit in a few months.

Now, whenever I turn my head-unit off or on, the sub makes a very loud BOOM-BUM sound. And the same sound when I switch cds. When I have a cd playing and i turn the volume to 0, I can hear the sub rumbling.

Because I am using the factory head-unit, a converter was needed to convert the speaker level outs (I think thats what it is called) to rca. The installer told me this was creating noise on the line, which is amplified by the amp, and causes the loud noise I hear. He said this will go away when I replace the head-unit with one that has rca outs.

Specs are:
Car:  2002 Celica
Amp : Kenwood KAC-629S (350 watt x 1)
Sub : Kenwood KFC-W3005 (12 inch Peak Input 700W  Rated Input 172W) in a ported box.
The wiring Kit and rca converter are Stinger.

Questions:
Is there an easy fix?
Should I just buy an aftermarket head-unit, and will it resolve the loud noise and the rumbling?

Thanks for any help.

g

I took out the factory HU and put a Kenwood KDC-X859 in place of it. Now all the problems are gone. Seems the speaker level to Line level converter was creating the noise.