Living right next to the landlords son is a BAD thing! A couple suggestions:
Get an Auralex GRAMMA, this will help cut down on vibrations going through the floor and walls. Mopads for your stereo speakers/studio monitors too.
Observe the 12:00 to 10:00 rule, no noise from noon to ten o'clock, and turn it down even lower after 8:00
Talk to your neighbors, it's amazing what this will accomplish! I live in an apartment, and I've had my entire band practice in my living room every weekend for years (at a subdued level of course, hand drums, vocal PA, plugged-in acoustics, and a small bass amp). I got away with this because I knew my neighbors!!!!!!
No offense to Slayer fans, to each his/her own, but understand if you don't like Slayer, it sounds like noise. Loud, grating, headache-causing noise. If you don't like this kind of music, it reaches the annoying level after about ten minutes. (Not judging taste, just saying)
Get a pair of headphones
Move somewhere where your landlords son isn't reporting on you!
Good luck!