As I don't want to get in big argument here... I'll just say that speaker positioning is the key of a good sounding system. In acoustics is of big importance which way sound is going to bounce, and what material is that sound is bouncing of... In general sound waves are reflected by hard surfaces and absorbed by soft ones, but most materials absorb and reflect high-frequency (treble) and low-frequency (bass) sounds differently. Hatch plastics will rattle if the bass level is high enough to make them vibrate. Expandable foam has been used quite often to stop unwanted rattling... Inside and outside of the vehicle.
no argument, (I compete in car audio comps), I understand what your saying, though lower bass frequencies are not directional as opposed to mid and highs, which are. That's when its critical on placement for staging. The question was more would you get harmonics from the glass moving and plastic's rattling with the sub firing directly at the hatch glass, to effect the sound quality? (don't forget to add in that sound bouncing, off different types of materials will alter the bounced frequency and also the sound wave timing with the rest of the system).
This is in a 2+2 so not totally relevant, but I love this setup No rattles in any plastic but I had to screw cardboard between the where the rear speaker screws into the body to eliminate vibrations at really low frequencies Pioneer 680 Watt Amp for door and rear speakers and 1000 watt pioneer mono amp for the subs
