This is a very common problem with 3 pick up strats. Every time the sting vibrates near the pickup it is attracted to the magnet which creates that crap sound your talking about. The solution is easy just lower the pickups until you get a clean tone. Normally the bass side will be lower than the treble.
You might also want to adjust the polepices on the pickups as well to get the most tone of of your guitar.
fell free to send me an e-mail
and ill send you a diagram on pole pice adjustment.
I couldn’t work out how to post it