Turn-on pops are common, unfortunately. There can be lots of casues... Everything from a faulty install to a poor ground, to gains set to high, to "flea-market" gear.... It would be anybody's guess based on your post.
There are a few super guys who ang out here who can help you make a proper diagnosis. Tell us what equipment you have, how it is connected, and what your basic settings, (gains, crossovers, etc) are and we can give you a better idea of what might be the problem. Otherwise, you are going to get nothing but guesses.
Let us know!