hey dude how's it going? I've heard of the popping noise problem a few times now, mainly because i looked into it when my car was suffering from a hardcore version where as soon as i turned it on one of my speakers made a popping noise the equivalent if not louder than a balloon being popped in the car several time a second and wouldn't stop(small enclosed space noise reverberates like crazy). I was doing it at 5:30 in the morning installing my amp and when i test ran it it went from nice music to massive popping noises and scared the cr*p out of me. Suprised i didn't wake the parents. I've mostly fixed it now, but just today got a singular popping noise when driving - once again, very loud, scared the crap out of me. I localised it back to the rear left hand speaker, i'm going to be pulling it out again and running tape around all the speaker wire leading down towards the amp and make sure there's no contact with the parcel shelf metal as i believe this may have been the problem and taping around the speaker wires near the parcel shelf metal appeared to fix it the first time.
Anyway, for your situation however where it's just with the turn on it's not uncommon. I have it in my car too. It's to do with the order in which the headunit and amplifier power up. As others here have stated, the amplifier should power up AFTER the headunit and power down BEFORE the headunit. Some amplifiers have this feature built in. Take a look at the oldschool Soundstream Tarantula amplifiers. These have what they have named "Drive Delay 2" Technology to ensure the amp powers up after the headunit and powers down before the headunit. I've put a link below, look at page 5.
http://www.soundstream.com/manuals/AMP/tarantula.pdf
However, for those of us who can't afford an oldschool Tarantula (or just bought a Soundstream PCA3500D instead) there is another solution
. I can't remember exactly how it's done but with a bit of searching on both here and
www.caraudioaustralia.com you should be able to dig it up. I think it involves placing a low impedence resistor (i could be completely wrong, but i know it's some small electrical component) on your speaker lines or something similar which causes the slight delay to occur and stop the popping or something. To be honest, i don't remember exactly but i know the information is out there. If you still can't find it after a search on these two forums get back to me and i'll try and dig it up for you.
Cheers, Bryce.